feat: Initialize backend with NestJS framework and serial communication

- Added package.json for backend dependencies and scripts.
- Implemented basic AppController and AppService with a simple "Hello World!" endpoint.
- Created SerialModule for handling serial communication with the Pico.
- Developed SerialController and SerialService to manage serial ports and commands.
- Implemented event streaming for serial data.
- Added Jest tests for AppController and e2e tests for the application.
- Set up TypeScript configuration for the backend.
- Created frontend SendBox component for sending commands to the backend.
- Established Pico firmware for controlling a stepper motor via serial commands.
- Documented project structure and usage in README files.

pico/.gitignore

@@ -0,0 +1,5 @@
+.pio
+.vscode/.browse.c_cpp.db*
+.vscode/c_cpp_properties.json
+.vscode/launch.json
+.vscode/ipch

pico/.vscode/extensions.json

@@ -0,0 +1,10 @@
+{
+    // See http://go.microsoft.com/fwlink/?LinkId=827846
+    // for the documentation about the extensions.json format
+    "recommendations": [
+        "platformio.platformio-ide"
+    ],
+    "unwantedRecommendations": [
+        "ms-vscode.cpptools-extension-pack"
+    ]
+}

pico/README_PICO_SERIAL.md

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+# Pico Serial Motor Control Integration
+
+This project enables a Raspberry Pi Pico to be controlled via serial commands from a TypeScript backend. The Pico firmware parses commands received over serial and controls a stepper motor accordingly, while also sending log/status messages back.
+
+## Serial Commands Supported
+- `STEP <steps> <direction>`: Move the motor by the specified number of steps. Direction: 1 for forward, 0 for reverse.
+- `SPEED <delay_us>`: Set the motor speed (delay in microseconds between steps).
+- `LOG <message>`: Print a log message to serial.
+
+## Firmware Files
+- `src/main.cpp`: Main firmware logic, serial command parsing, motor control, logging.
+- `src/ULN2003Stepper.h`, `src/Stepper.h`: Stepper motor driver classes.
+
+## How to Extend
+- Add new serial commands by updating the parser in `main.cpp`.
+- Implement additional motor features or logging as needed.
+- Ensure any new global variables are only defined in one source file, and declared as `extern` elsewhere.
+
+## TypeScript Backend
+- Use a library like `serialport` to communicate with the Pico.
+- Send commands as plain text terminated by `\n`.
+- Read and process log/status messages from serial.
+
+## Example Serial Session
+```
+SPEED 3000
+STEP 4096 1
+LOG Motor moved
+```
+
+## Build & Upload
+Use PlatformIO to build and upload the firmware to the Pico.
+
+---
+This README is intended for another developer or Copilot to implement further changes or features.

pico/include/README

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+
+This directory is intended for project header files.
+
+A header file is a file containing C declarations and macro definitions
+to be shared between several project source files. You request the use of a
+header file in your project source file (C, C++, etc) located in `src` folder
+by including it, with the C preprocessing directive `#include'.
+
+```src/main.c
+
+#include "header.h"
+
+int main (void)
+{
+ ...
+}
+```
+
+Including a header file produces the same results as copying the header file
+into each source file that needs it. Such copying would be time-consuming
+and error-prone. With a header file, the related declarations appear
+in only one place. If they need to be changed, they can be changed in one
+place, and programs that include the header file will automatically use the
+new version when next recompiled. The header file eliminates the labor of
+finding and changing all the copies as well as the risk that a failure to
+find one copy will result in inconsistencies within a program.
+
+In C, the convention is to give header files names that end with `.h'.
+
+Read more about using header files in official GCC documentation:
+
+* Include Syntax
+* Include Operation
+* Once-Only Headers
+* Computed Includes
+
+https://gcc.gnu.org/onlinedocs/cpp/Header-Files.html

pico/lib/README

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+
+This directory is intended for project specific (private) libraries.
+PlatformIO will compile them to static libraries and link into the executable file.
+
+The source code of each library should be placed in a separate directory
+("lib/your_library_name/[Code]").
+
+For example, see the structure of the following example libraries `Foo` and `Bar`:
+
+|--lib
+|  |
+|  |--Bar
+|  |  |--docs
+|  |  |--examples
+|  |  |--src
+|  |     |- Bar.c
+|  |     |- Bar.h
+|  |  |- library.json (optional. for custom build options, etc) https://docs.platformio.org/page/librarymanager/config.html
+|  |
+|  |--Foo
+|  |  |- Foo.c
+|  |  |- Foo.h
+|  |
+|  |- README --> THIS FILE
+|
+|- platformio.ini
+|--src
+   |- main.c
+
+Example contents of `src/main.c` using Foo and Bar:
+```
+#include <Foo.h>
+#include <Bar.h>
+
+int main (void)
+{
+  ...
+}
+
+```
+
+The PlatformIO Library Dependency Finder will find automatically dependent
+libraries by scanning project source files.
+
+More information about PlatformIO Library Dependency Finder
+- https://docs.platformio.org/page/librarymanager/ldf.html

pico/platformio.ini

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+; PlatformIO Project Configuration File
+;
+;   Build options: build flags, source filter
+;   Upload options: custom upload port, speed and extra flags
+;   Library options: dependencies, extra library storages
+;   Advanced options: extra scripting
+;
+; Please visit documentation for the other options and examples
+; https://docs.platformio.org/page/projectconf.html
+
+[env:pico]
+platform = raspberrypi
+board = pico
+framework = arduino
+; build_flags removed, no longer needed

pico/src/Stepper.h

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+#pragma once
+// ...existing code...
+class Stepper {
+protected:
+    int steps_per_rev;
+public:
+    virtual void step(int steps, bool direction) = 0;
+    void step_rev(int revs, bool direction){
+        step(steps_per_rev*revs, direction);
+    }
+    int get_steps_per_rev(){
+        return steps_per_rev;
+    }
+    virtual ~Stepper() {}
+};

pico/src/ULN2003Stepper.h

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+#pragma once
+#include <Arduino.h>
+#include "Stepper.h"
+#include <array>
+class ULN2003Stepper : public Stepper {
+private:
+    std::array<uint8_t, 4> pins;
+    static constexpr int steps_per_seq = 8;
+    const uint8_t sequence[8][4] = {
+        {1, 0, 0, 0},
+        {1, 1, 0, 0},
+        {0, 1, 0, 0},
+        {0, 1, 1, 0},
+        {0, 0, 1, 0},
+        {0, 0, 1, 1},
+        {0, 0, 0, 1},
+        {1, 0, 0, 1}
+    };
+    int step_delay_us = 5000;
+public:
+    ULN2003Stepper(std::array<uint8_t, 4> pins, int rev_steps) : pins(pins) {
+        steps_per_rev = rev_steps;
+        for (auto pin : pins) {
+            pinMode(pin, OUTPUT);
+        }
+    }
+    void step(int steps, bool direction) override {
+        for (int i = 0; i < steps; ++i) {
+            int seq_idx = direction ? (i % steps_per_seq) : (steps_per_seq - 1 - (i % steps_per_seq));
+            for (int j = 0; j < 4; ++j) {
+                digitalWrite(pins[j], sequence[seq_idx][j]);
+            }
+            delayMicroseconds(step_delay_us);
+        }
+    }
+    void setSpeed(int delay_us) {
+        step_delay_us = delay_us;
+    }
+};

pico/src/main.cpp

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+#include <Arduino.h>
+#include "Stepper.h"
+#include "ULN2003Stepper.h"
+
+
+ULN2003Stepper driver1({18, 19, 20, 21}, 4096);
+int revSteps = 0;
+
+void setup() {
+  Serial.begin(115200);
+  revSteps = driver1.get_steps_per_rev();
+  Serial.print("Steps: ");
+  Serial.println(revSteps);
+}
+
+void loop() {
+  static String input = "";
+  while (Serial.available()) {
+    char c = Serial.read();
+    if (c == '\n' || c == '\r') {
+      if (input.length() > 0) {
+        Serial.print("Received: ");
+        Serial.println(input);
+        // Parse command
+        if (input.startsWith("STEP ")) {
+          int idx1 = input.indexOf(' ');
+          int idx2 = input.indexOf(' ', idx1 + 1);
+          int steps = input.substring(idx1 + 1, idx2).toInt();
+          int dir = input.substring(idx2 + 1).toInt();
+          driver1.step(steps, dir != 0);
+          Serial.print("Motor moved ");
+          Serial.print(steps);
+          Serial.print(" steps in direction ");
+          Serial.println(dir);
+        } else if (input.startsWith("SPEED ")) {
+          int delay_us = input.substring(6).toInt();
+          driver1.setSpeed(delay_us);
+          Serial.print("Speed set to ");
+          Serial.println(delay_us);
+        } else if (input.startsWith("LOG ")) {
+          Serial.print("LOG: ");
+          Serial.println(input.substring(4));
+        } else {
+          Serial.println("Unknown command");
+        }
+        input = "";
+      }
+    } else {
+      input += c;
+    }
+  }
+  delay(10); // avoid busy loop
+}

pico/test/README

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+
+This directory is intended for PlatformIO Test Runner and project tests.
+
+Unit Testing is a software testing method by which individual units of
+source code, sets of one or more MCU program modules together with associated
+control data, usage procedures, and operating procedures, are tested to
+determine whether they are fit for use. Unit testing finds problems early
+in the development cycle.
+
+More information about PlatformIO Unit Testing:
+- https://docs.platformio.org/en/latest/advanced/unit-testing/index.html