Add GitHub Actions CI for Arduino sketch compilation

- Test compilation on Arduino Uno, ESP8266, and ESP32 boards
- Verify both ir_sender and ir_receiver sketches build successfully
- Install IRremote library v4.1.2 as required by the code
- Run on all pushes and pull requests

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: claude

.github/workflows/arduino-build.yml

@@ -0,0 +1,57 @@
+name: Arduino Build CI
+
+on:
+  push:
+    branches: [ "**" ]
+  pull_request:
+    branches: [ "**" ]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        sketch:
+          - ac_control/ir_sender/ir_sender.ino
+          - ac_control/ir_receiver/ir_receiver.ino
+        board:
+          - fqbn: "arduino:avr:uno"
+            platform: "arduino:avr"
+            name: "Arduino Uno"
+          - fqbn: "esp8266:esp8266:nodemcuv2"
+            platform: "esp8266:esp8266"
+            platform-url: "https://arduino.esp8266.com/stable/package_esp8266com_index.json"
+            name: "ESP8266"
+          - fqbn: "esp32:esp32:esp32"
+            platform: "esp32:esp32"
+            platform-url: "https://raw.githubusercontent.com/espressif/arduino-esp32/gh-pages/package_esp32_index.json"
+            name: "ESP32"
+
+    steps:
+    - name: Checkout repository
+      uses: actions/checkout@v4
+
+    - name: Setup Arduino CLI
+      uses: arduino/setup-arduino-cli@v1
+
+    - name: Install Arduino platform
+      run: |
+        if [ -n "${{ matrix.board.platform-url }}" ]; then
+          arduino-cli config init
+          arduino-cli config add board_manager.additional_urls ${{ matrix.board.platform-url }}
+        fi
+        arduino-cli core update-index
+        arduino-cli core install ${{ matrix.board.platform }}
+
+    - name: Install IRremote library
+      run: |
+        arduino-cli lib install "[email protected]"
+
+    - name: Compile sketch for ${{ matrix.board.name }}
+      run: |
+        arduino-cli compile --fqbn ${{ matrix.board.fqbn }} ${{ matrix.sketch }}
+
+    - name: Build summary
+      run: |
+        echo "✅ Successfully built ${{ matrix.sketch }} for ${{ matrix.board.name }}"