Install ffmpeg in integration-tests CI job

https://claude.ai/code/session_0161hwiY52dSwBergfZmniKA

Author: claude

.github/workflows/ci.yml

@@ -38,6 +38,9 @@ jobs:
       - name: Install dependencies
         run: pnpm install
 
+      - name: Install ffmpeg
+        run: sudo apt-get install -y ffmpeg
+
       - name: Install Playwright Chromium
         run: pnpm --filter @git-glimpse/core exec playwright install chromium --with-deps