fix: file @ autocomplete performance using fd

- Replace slow synchronous directory walking with fd for fuzzy file search
- Auto-download fd to ~/.pi/agent/tools/ if not found in PATH
- Performance improved from ~900ms to ~10ms per keystroke on large repos
- Remove minimatch dependency from tui package
- Graceful degradation if fd unavailable (empty results)

Fixes #69

packages/tui/package.json

@@ -41,7 +41,6 @@
 		"chalk": "^5.5.0",
 		"marked": "^15.0.12",
 		"mime-types": "^3.0.1",
-		"minimatch": "^10.1.1",
 		"string-width": "^8.1.0"
 	},
 	"devDependencies": {