feat(coding-agent): implement hooks system

- Add hooks infrastructure in core/hooks/ (loader, runner, types)
- HookUIContext interface with mode-specific implementations
- Interactive mode: TUI-based selector/input/confirm dialogs
- RPC mode: JSON protocol for hook UI requests/responses
- Print mode: no-op UI context (hooks run but can't prompt)
- AgentSession.branch() now async, returns { selectedText, skipped }
- Settings: hooks[] and hookTimeout configuration
- Export hook types from package for hook authors

Based on PR #147 proposal, adapted for new architecture.

packages/coding-agent/package.json

@@ -33,7 +33,8 @@
 		"@mariozechner/pi-tui": "^0.17.0",
 		"chalk": "^5.5.0",
 		"diff": "^8.0.2",
-		"glob": "^11.0.3"
+		"glob": "^11.0.3",
+		"jiti": "^2.6.1"
 	},
 	"devDependencies": {
 		"@types/diff": "^7.0.2",