feat(extension): simplify command bar popup UI
- Minimal UI matching desktop cmd panel style (dark, transparent input)
- Commands: tag, note, search with inline autocomplete
- UI closes immediately on Enter (fire-and-forget)
- Backend saves async via datastore, decoupled from UI
- Removed dropdown/results for now - just input field
- Uses Playwright for dev launch (Google Chrome blocks --load-extension)
Usage: yarn extension:chrome
Then Option+P or click extension icon
Type: "tag foo, bar" or "note my note" and Enter