feat(coding-agent): add hook API for CLI flags, shortcuts, and tool control

Hook API additions:
- pi.getTools() / pi.setTools(toolNames) - dynamically enable/disable tools
- pi.registerFlag(name, options) / pi.getFlag(name) - register custom CLI flags
- pi.registerShortcut(shortcut, options) - register keyboard shortcuts

Plan mode hook (examples/hooks/plan-mode.ts):
- /plan command or Shift+P shortcut to toggle
- --plan CLI flag to start in plan mode
- Read-only tools: read, bash, grep, find, ls
- Bash restricted to non-destructive commands (blocks rm, mv, git commit, etc.)
- Interactive prompt after each response: execute, stay, or refine
- Shows plan indicator in footer when active
- State persists across sessions

packages/coding-agent/src/modes/interactive/components/custom-editor.ts

@@ -12,6 +12,8 @@ export class CustomEditor extends Editor {
 	public onEscape?: () => void;
 	public onCtrlD?: () => void;
 	public onPasteImage?: () => void;
+	/** Handler for hook-registered shortcuts. Returns true if handled. */
+	public onHookShortcut?: (data: string) => boolean;
 
 	constructor(theme: EditorTheme, keybindings: KeybindingsManager) {
 		super(theme);
@@ -26,6 +28,11 @@ export class CustomEditor extends Editor {
 	}
 
 	handleInput(data: string): void {
+		// Check hook-registered shortcuts first
+		if (this.onHookShortcut?.(data)) {
+			return;
+		}
+
 		// Check for Ctrl+V to handle clipboard image paste
 		if (matchesKey(data, "ctrl+v")) {
 			this.onPasteImage?.();