Custom tools with session lifecycle, examples for hooks and tools

- Custom tools: TypeScript modules that extend pi with new tools
  - Custom TUI rendering via renderCall/renderResult
  - User interaction via pi.ui (select, confirm, input, notify)
  - Session lifecycle via onSession callback for state reconstruction
  - Examples: todo.ts, question.ts, hello.ts

- Hook examples: permission-gate, git-checkpoint, protected-paths

- Session lifecycle centralized in AgentSession
  - Works across all modes (interactive, print, RPC)
  - Unified session event for hooks (replaces session_start/session_switch)

- Box component added to pi-tui

- Examples bundled in npm and binary releases

Fixes #190

packages/tui/README.md

@@ -8,7 +8,7 @@ Minimal terminal UI framework with differential rendering and synchronized outpu
 - **Synchronized Output**: Uses CSI 2026 for atomic screen updates (no flicker)
 - **Bracketed Paste Mode**: Handles large pastes correctly with markers for >10 line pastes
 - **Component-based**: Simple Component interface with render() method
-- **Built-in Components**: Text, Input, Editor, Markdown, Loader, SelectList, Spacer, Image
+- **Built-in Components**: Text, Input, Editor, Markdown, Loader, SelectList, Spacer, Image, Box, Container
 - **Inline Images**: Renders images in terminals that support Kitty or iTerm2 graphics protocols
 - **Autocomplete Support**: File paths and slash commands
 
@@ -75,6 +75,20 @@ container.addChild(component);
 container.removeChild(component);
 ```
 
+### Box
+
+Container that applies padding and background color to all children.
+
+```typescript
+const box = new Box(
+	1,                  // paddingX (default: 1)
+	1,                  // paddingY (default: 1)
+	(text) => chalk.bgGray(text)  // optional background function
+);
+box.addChild(new Text("Content", 0, 0));
+box.setBgFn((text) => chalk.bgBlue(text));  // Change background dynamically
+```
+
 ### Text
 
 Displays multi-line text with word wrapping and padding.