WIP: Add hook API for dynamic tool control with plan-mode hook example

- Add pi.getTools() and pi.setTools(toolNames) to HookAPI
- Hooks can now enable/disable tools dynamically
- Changes take effect on next agent turn

New example hook: plan-mode.ts
- Claude Code-style read-only exploration mode
- /plan command toggles plan mode on/off
- Plan mode tools: read, bash, grep, find, ls
- Edit/write tools disabled in plan mode
- Injects context telling agent about restrictions
- After each response, prompts to execute/stay/refine
- State persists across sessions

packages/coding-agent/examples/hooks/README.md

@@ -16,6 +16,7 @@ cp permission-gate.ts ~/.pi/agent/hooks/
 
 | Hook | Description |
 |------|-------------|
+| `plan-mode.ts` | Claude Code-style plan mode for read-only exploration with `/plan` command |
 | `permission-gate.ts` | Prompts for confirmation before dangerous bash commands (rm -rf, sudo, etc.) |
 | `git-checkpoint.ts` | Creates git stash checkpoints at each turn for code restoration on branch |
 | `protected-paths.ts` | Blocks writes to protected paths (.env, .git/, node_modules/) |