Add CI workflow: type-check and build Android APK

Runs bun --cwd client run build (tsc -b) on push/PR, then builds the
APK via build-apk.sh and uploads it as a workflow artifact. Also
compatible with Gitea Actions, which reads .github/workflows/ in
addition to .gitea/workflows/.

.github/workflows/ci.yml

@@ -0,0 +1,40 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+  workflow_dispatch:
+
+jobs:
+  typecheck:
+    name: Type-Check
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: oven-sh/setup-bun@v2
+        with:
+          bun-version: latest
+
+      - name: Install dependencies
+        run: bun install
+
+      - name: Type-check client
+        run: bun --cwd client run build
+
+  build-apk:
+    name: Build Android APK
+    runs-on: ubuntu-latest
+    needs: typecheck
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Build APK via Dockerfile.android
+        run: ./build-apk.sh
+
+      - uses: actions/upload-artifact@v4
+        with:
+          name: tiptoi-sync-apk
+          path: apk-output/tiptoi-sync.apk