chore: gitignore playwright-mcp scratch and final-check.png

The local agent loop drops:
- a `.playwright-mcp/` directory full of intermediate screenshots while
  debugging browser sessions
- a `final-check.png` of the page state at the end of a task

Both are local-only debugging artifacts that should never end up in a
commit. Add them next to the existing `screenshot-*.png` / `full-UI.png`
rules so the same dev-loop garbage collection pattern continues to hold
without anyone having to think about it.

.gitignore

@@ -28,6 +28,12 @@ copilot-instructions.md
 # Generated screenshots and transient artifacts
 screenshot-*.png
 full-UI.png
+# Playwright MCP scratch — directory + ad-hoc PNGs the agent drops while
+# debugging browser sessions. /final-check.png is the convention used by the
+# local agent loop for a one-off end-of-task verification grab; ignore
+# either way so they never sneak into a commit.
+.playwright-mcp/
+final-check.png
 
 # Version file written by Docker/CI build — generated, never committed
 api/_version.py