Add led-matrix-painter (#5)

* Add led-matrix-painter example

* update readme

* update license

* fix uint definition

---------

Co-authored-by: Dario Sammaruga <d.sammaruga@ext.arduino.cc>

Author: BeanRepo

examples/led-matrix-painter/README.md

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+# LED Matrix Painter
+
+The **LED Matrix Painter** example provides a web-based tool for designing frames and animations for the Arduino UNO Q 8×13 LED matrix. You can create individual frames, organize them into animations, preview them in real-time on the board, and export them as C++ code.
+
+![LED Matrix Painter](assets/docs_assets/led-matrix-painter.png)
+
+## Description
+
+This example allows you to design LED matrix frames using an interactive web interface. Each frame can have custom brightness levels (0-7) for each LED pixel. You can:
+
+- **Design frames** with pixel-by-pixel control using an interactive grid
+- **Preview in real-time** on the Arduino UNO Q LED matrix
+- **Save and organize** multiple frames with a persistent database
+- **Create animations** by sequencing multiple frames together
+- **Export code** as C++ arrays ready to use in your Arduino sketches
+- **Transform frames** with operations like invert, rotate, and flip
+
+The application uses the Router Bridge to communicate between the web interface (running on Linux) and the Arduino sketch (running on the microcontroller), enabling real-time updates to the physical LED matrix.
+
+## Bricks Used
+
+- `web_ui`: Provides the web server and HTTP API endpoints for the interactive frame designer interface.
+- `dbstorage_sqlstore` (implicit): Stores frame data persistently in a SQLite database.
+
+## Hardware and Software Requirements
+
+### Hardware
+
+- Arduino UNO Q (x1)
+- USB-C® cable (for power and programming) (x1)
+
+### Software
+
+- Arduino App Lab
+
+## How to Use the Example
+
+1. Launch the App by clicking the **Play** button in the top-right corner. Wait until the App has launched.
+2. **Design a frame:**
+   - Click on individual pixels in the 8×13 grid to toggle them on/off
+   - Use the brightness slider to adjust LED intensity (0-7)
+   - Click on pixels with different brightness values to paint with varying intensities
+3. **Save your frame:**
+   - Click the **Save Frame** button to persist the current design
+   - Frames are automatically saved to a database and appear in the sidebar
+4. **Create animations:**
+   - Save multiple frames
+   - Switch to **Animations** mode in the sidebar
+   - Create a new animation and add frames to it
+   - Use **Play** to preview the animation on the board
+5. **Export code:**
+   - Select the frames or animations you want to export
+   - Click **Export** to generate C++ code
+   - Copy the generated arrays into your Arduino sketch
+
+## How it Works
+
+The LED Matrix Painter consists of three main components working together:
+
+- **Web Interface (Frontend)**: An interactive grid editor built with HTML/CSS/JavaScript that sends pixel data to the backend via HTTP API calls.
+
+- **Python Backend**: Handles frame storage in a SQLite database, manages frame transformations, and communicates with the Arduino via Router Bridge.
+
+- **Arduino Sketch**: Receives frame data over Router Bridge and displays it on the physical LED matrix using the `Arduino_LED_Matrix` library.
+
+High-level data flow:
+
+```
+Web Browser → HTTP API → Python Backend → Router Bridge → Arduino LED Matrix
+                              ↓
+                        SQLite Database
+```
+
+The workflow:
+1. User edits a frame in the web interface
+2. Changes are sent to Python backend via HTTP POST
+3. Backend validates and stores the frame in SQLite
+4. Backend sends frame data to Arduino via Bridge
+5. Arduino sketch renders the frame on the LED matrix
+
+## Understanding the Code
+
+### 🔧 Backend (`main.py`)
+
+The Python application manages the HTTP API, database operations, and communication with the Arduino.
+
+- **`designer = FrameDesigner()`**: Initializes the frame designer utility from `arduino.app_utils`, which provides transformation operations (invert, rotate, flip).
+
+- **`store.init_db()`**: Creates the SQLite database and tables for storing frames if they don't exist.
+
+- **`ui.expose_api('POST', '/persist_frame', persist_frame)`**: Exposes an HTTP endpoint that saves or updates frames in the database.
+
+- **`ui.expose_api('POST', '/load_frame', load_frame)`**: Loads a frame from the database by ID or retrieves the last edited frame.
+
+- **`ui.expose_api('GET', '/list_frames', list_frames)`**: Returns all saved frames for display in the sidebar.
+
+- **`ui.expose_api('POST', '/play_animation', play_animation)`**: Sends a sequence of frames to the Arduino to play as an animation.
+
+- **`ui.expose_api('POST', '/export_frames', export_frames)`**: Generates C++ code arrays from selected frames for use in Arduino sketches.
+
+- **`Bridge.call("draw", frame_bytes)`**: Sends frame data to the Arduino sketch to update the LED matrix display.
+
+- **`AppFrame` class**: Custom extension of `arduino.app_utils.Frame` that adds metadata like frame name, position, duration, and database persistence methods.
+
+### 💻 Frontend (`app.js` + `index.html`)
+
+The web interface provides an interactive pixel grid editor and frame management tools.
+
+- **Pixel Grid**: An 8×13 canvas that responds to mouse clicks and drag operations for painting pixels.
+
+- **Brightness Control**: A slider (0-7) that controls the current brush brightness level.
+
+- **Frame List**: Displays all saved frames in a sidebar with options to load, delete, or reorder them.
+
+- **Animations Mode**: Allows creating and managing animation sequences by dragging frames into animation containers.
+
+- **Transform Tools**: Buttons for applying transformations (invert, rotate 180°, flip horizontal/vertical).
+
+- **Export Modal**: Generates and displays C++ code for selected frames or animations.
+
+- **HTTP API calls**: Uses `fetch()` to communicate with the Python backend for all frame operations (save, load, delete, transform, export, play).
+
+### 🔧 Hardware (`sketch.ino`)
+
+The Arduino code handles LED matrix control and Router Bridge communication.
+
+- **`matrix.begin()`**: Initializes the Arduino_LED_Matrix library for controlling the UNO Q LED matrix.
+
+- **`matrix.setGrayscaleBits(8)`**: Configures the matrix to accept 8-bit brightness values (0-255) for each pixel.
+
+- **`Bridge.begin()`**: Initializes Router Bridge for receiving commands from the Python application.
+
+- **`Bridge.provide("draw", draw)`**: Registers the `draw` function to be callable from Python, which accepts frame data and renders it on the matrix.
+
+- **`Bridge.provide("play_animation", play_animation)`**: Registers the animation playback function that accepts multiple frames and plays them sequentially.
+
+- **`matrix.draw(frame.data())`**: Renders a single frame on the LED matrix using raw byte data.
+
+- **`matrix.loadWrapper()` + `matrix.playSequence()`**: Loads an animation sequence and plays it on the LED matrix.
+
+## Frame Data Format
+
+Frames are stored as 8×13 arrays where each value represents LED brightness (0-255):
+
+```cpp
+// Example frame in C++ format
+const uint8_t frame[][12] = {
+  {255, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 255},
+  {0, 255, 0, 0, 0, 0, 0, 0, 0, 0, 255, 0},
+  // ... 6 more rows
+};
+```
+
+For animations, frames are stored as `uint32_t` arrays compatible with the Arduino_LED_Matrix library:
+
+```cpp
+const uint32_t animation[][5] = {
+  {0x12345678, 0x9abcdef0, 0x12345678, 0x9abcdef0, 1000},  // Frame 1, 1000ms duration
+  {0xfedcba98, 0x76543210, 0xfedcba98, 0x76543210, 1000},  // Frame 2, 1000ms duration
+};
+```

examples/led-matrix-painter/app.yaml

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+name: Led Matrix Painter
+icon: 🟦
+description:
+  This example shows how to create a tool to design frames for an LED matrix using Arduino.
+  It provides a web interface where users can design frames and animations and export them as C/C++ code.
+
+bricks:
+  - arduino:web_ui
+  - arduino:dbstorage_sqlstore