feat: open quick settings before full VS Code settings

[auchan]

Summary

• the ⚙ gear now opens the in-chat quick Settings panel (the original simple toggles: auto-compaction, auto-retry, show images, auto-collapse tool results, auto-attach active file)
• the quick panel gained an "Open full VS Code settings…" button that closes the overlay and opens the native VS Code Settings filtered to @ext:auchan.pion-code

Validation

• bun run check-types
• bun run lint
• bun run compile-tests
• focused VS Code settings entry tests (3 passing)
• git diff --check