fix(ci): provision google-credentials.json before release build

include_str! embeds google-credentials.json at compile time, but the
file is gitignored, so CI checkouts had no file and the Rust crate
failed to compile on all three platforms. Write it from the
GOOGLE_CREDENTIALS secret, falling back to the committed example
placeholders so the build always succeeds.

.github/workflows/release.yml

@@ -137,6 +137,19 @@ jobs:
       - name: Install frontend dependencies
         run: pnpm install --frozen-lockfile
 
+      - name: Provision Google credentials
+        shell: bash
+        env:
+          GOOGLE_CREDENTIALS: ${{ secrets.GOOGLE_CREDENTIALS }}
+        run: |
+          if [ -n "$GOOGLE_CREDENTIALS" ]; then
+            printf '%s' "$GOOGLE_CREDENTIALS" > google-credentials.json
+            echo "Wrote google-credentials.json from GOOGLE_CREDENTIALS secret."
+          else
+            cp google-credentials.example.json google-credentials.json
+            echo "::warning::GOOGLE_CREDENTIALS secret not set — embedding placeholder credentials; Google Drive backup will be disabled in this release."
+          fi
+
       - name: Build and upload
         uses: tauri-apps/tauri-action@v0
         env: