ci: move Android APK build out of PR gate into dedicated workflow

The full Gradle build is heavy for every PR push. Keep only typecheck +
lint as the PR gate; run the APK build on main pushes and manual dispatch.

Co-authored-by: Orca <help@stably.ai>

.github/workflows/mobile-build.yml

@@ -0,0 +1,46 @@
+name: Mobile Build
+
+on:
+  push:
+    branches:
+      - main
+    paths:
+      - 'mobile/**'
+  workflow_dispatch:
+
+jobs:
+  android-build:
+    runs-on: ubuntu-latest
+
+    defaults:
+      run:
+        working-directory: mobile
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version-file: .nvmrc
+
+      - name: Setup pnpm
+        uses: pnpm/action-setup@v4
+        with:
+          run_install: false
+
+      - name: Install dependencies
+        run: pnpm install --frozen-lockfile
+
+      - name: Setup JDK 17
+        uses: actions/setup-java@v4
+        with:
+          distribution: temurin
+          java-version: 17
+
+      - name: Expo prebuild
+        run: npx expo prebuild --platform android --no-install
+
+      - name: Build Android debug APK
+        run: cd android && ./gradlew assembleDebug

.github/workflows/mobile.yml

@@ -41,39 +41,3 @@ jobs:
       - name: Lint
         run: pnpm lint
 
-  android-build:
-    runs-on: ubuntu-latest
-    needs: verify
-
-    defaults:
-      run:
-        working-directory: mobile
-
-    steps:
-      - name: Checkout
-        uses: actions/checkout@v4
-
-      - name: Setup Node.js
-        uses: actions/setup-node@v4
-        with:
-          node-version-file: .nvmrc
-
-      - name: Setup pnpm
-        uses: pnpm/action-setup@v4
-        with:
-          run_install: false
-
-      - name: Install dependencies
-        run: pnpm install --frozen-lockfile
-
-      - name: Setup JDK 17
-        uses: actions/setup-java@v4
-        with:
-          distribution: temurin
-          java-version: 17
-
-      - name: Expo prebuild
-        run: npx expo prebuild --platform android --no-install
-
-      - name: Build Android debug APK
-        run: cd android && ./gradlew assembleDebug