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/src/modes/interactive/components/hook-selector.ts

@@ -0,0 +1,91 @@
+/**
+ * Generic selector component for hooks.
+ * Displays a list of string options with keyboard navigation.
+ */
+
+import { Container, Spacer, Text } from "@mariozechner/pi-tui";
+import { theme } from "../theme/theme.js";
+import { DynamicBorder } from "./dynamic-border.js";
+
+export class HookSelectorComponent extends Container {
+	private options: string[];
+	private selectedIndex = 0;
+	private listContainer: Container;
+	private onSelectCallback: (option: string) => void;
+	private onCancelCallback: () => void;
+
+	constructor(title: string, options: string[], onSelect: (option: string) => void, onCancel: () => void) {
+		super();
+
+		this.options = options;
+		this.onSelectCallback = onSelect;
+		this.onCancelCallback = onCancel;
+
+		// Add top border
+		this.addChild(new DynamicBorder());
+		this.addChild(new Spacer(1));
+
+		// Add title
+		this.addChild(new Text(theme.fg("accent", title), 1, 0));
+		this.addChild(new Spacer(1));
+
+		// Create list container
+		this.listContainer = new Container();
+		this.addChild(this.listContainer);
+
+		this.addChild(new Spacer(1));
+
+		// Add hint
+		this.addChild(new Text(theme.fg("dim", "↑↓ navigate  enter select  esc cancel"), 1, 0));
+
+		this.addChild(new Spacer(1));
+
+		// Add bottom border
+		this.addChild(new DynamicBorder());
+
+		// Initial render
+		this.updateList();
+	}
+
+	private updateList(): void {
+		this.listContainer.clear();
+
+		for (let i = 0; i < this.options.length; i++) {
+			const option = this.options[i];
+			const isSelected = i === this.selectedIndex;
+
+			let text = "";
+			if (isSelected) {
+				text = theme.fg("accent", "→ ") + theme.fg("accent", option);
+			} else {
+				text = "  " + theme.fg("text", option);
+			}
+
+			this.listContainer.addChild(new Text(text, 1, 0));
+		}
+	}
+
+	handleInput(keyData: string): void {
+		// Up arrow or k
+		if (keyData === "\x1b[A" || keyData === "k") {
+			this.selectedIndex = Math.max(0, this.selectedIndex - 1);
+			this.updateList();
+		}
+		// Down arrow or j
+		else if (keyData === "\x1b[B" || keyData === "j") {
+			this.selectedIndex = Math.min(this.options.length - 1, this.selectedIndex + 1);
+			this.updateList();
+		}
+		// Enter
+		else if (keyData === "\r" || keyData === "\n") {
+			const selected = this.options[this.selectedIndex];
+			if (selected) {
+				this.onSelectCallback(selected);
+			}
+		}
+		// Escape
+		else if (keyData === "\x1b") {
+			this.onCancelCallback();
+		}
+	}
+}