ci(mobile): retry bun install in mobile build workflow (#564)

Mirror the desktop-build retry loop so a transient tarball download
failure no longer fails the whole Android build.

.github/workflows/mobile-build.yml

@@ -68,7 +68,16 @@ jobs:
         uses: oven-sh/setup-bun@v2
 
       - name: Install release validation dependencies
-        run: bun install --frozen-lockfile
+        run: |
+          for attempt in 1 2 3; do
+            if bun install --frozen-lockfile; then
+              exit 0
+            fi
+            if [[ "$attempt" = "3" ]]; then
+              exit 1
+            fi
+            sleep "$((15 * attempt))"
+          done
 
       - name: Run full project regression tests
         run: bun run test
@@ -236,7 +245,16 @@ jobs:
           clean: true
 
       - name: Install dependencies
-        run: bun install --frozen-lockfile
+        run: |
+          for attempt in 1 2 3; do
+            if bun install --frozen-lockfile; then
+              exit 0
+            fi
+            if [[ "$attempt" = "3" ]]; then
+              exit 1
+            fi
+            sleep "$((15 * attempt))"
+          done
 
       - name: Check Expo dependencies
         run: |