ci: add build & test workflow

Runs on push to main / PRs / manual dispatch. Builds and tests the Swift
package (macOS + Xcode 26) and compiles the Buddy firmware via arduino-cli,
since the existing DMG workflow is manual-only and covers neither tests nor
the firmware.

Author: lltx

.github/workflows/ci.yml

@@ -0,0 +1,63 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+jobs:
+  swift-build-test:
+    name: Swift build & test
+    runs-on: macos-15
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Select Xcode 26
+        run: |
+          XCODE_APP="$(find /Applications -maxdepth 1 -name 'Xcode_26*.app' -type d | sort | tail -n 1)"
+          if [ -z "$XCODE_APP" ]; then
+            echo "Xcode 26 is required (SwiftUI #Preview macros need its toolchain plugin)"
+            exit 1
+          fi
+          sudo xcode-select -s "$XCODE_APP/Contents/Developer"
+
+      - name: Show toolchain
+        run: swift --version
+
+      - name: Build
+        run: swift build
+
+      - name: Test
+        run: swift test
+
+  firmware-compile:
+    name: Buddy firmware compile
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup arduino-cli
+        uses: arduino/setup-arduino-cli@v2
+
+      - name: Install ESP32 core
+        run: |
+          arduino-cli config init
+          arduino-cli config add board_manager.additional_urls https://espressif.github.io/arduino-esp32/package_esp32_index.json
+          arduino-cli core update-index
+          arduino-cli core install esp32:esp32
+
+      - name: Install libraries
+        run: |
+          arduino-cli lib install \
+            "Adafruit GFX Library" \
+            "Adafruit ST7735 and ST7789 Library" \
+            "Adafruit BusIO"
+
+      - name: Compile firmware
+        run: arduino-cli compile --fqbn esp32:esp32:esp32c6:CDCOnBoot=cdc,PartitionScheme=huge_app hardware