perf(ci): add Bun and Gradle caching to Android workflow

Cache Bun dependencies (install cache + node_modules) and Gradle caches
(wrapper, dependencies, build artifacts) to dramatically speed up CI builds.
Gradle key uses Cargo.lock since gradle files don't exist at checkout time.

Co-Authored-By: Claude <noreply@anthropic.com>

.github/workflows/android.yml

@@ -40,6 +40,18 @@ jobs:
         with:
           bun-version: latest
 
+      - name: Cache Bun dependencies
+        uses: actions/cache@v4
+        with:
+          path: |
+            ~/.bun/install/cache
+            node_modules
+            apps/*/node_modules
+            packages/*/node_modules
+          key: ${{ runner.os }}-bun-${{ hashFiles('bun.lock', '**/package.json') }}
+          restore-keys: |
+            ${{ runner.os }}-bun-
+
       - name: Install dependencies
         run: bun install
 
@@ -74,6 +86,17 @@ jobs:
           restore-keys: |
             ${{ runner.os }}-cargo-android-
 
+      - name: Cache Gradle
+        uses: actions/cache@v4
+        with:
+          path: |
+            ~/.gradle/caches
+            ~/.gradle/wrapper
+            apps/tauri/gen/android/.gradle
+          key: ${{ runner.os }}-gradle-android-${{ hashFiles('apps/tauri/Cargo.lock') }}
+          restore-keys: |
+            ${{ runner.os }}-gradle-android-
+
       - name: Install Tauri CLI
         run: cd apps/tauri && bun install