feat: implement hooks, plugins, session forks, and vim motions

Add 4 major features to codetyper-cli:

- Hooks System: Lifecycle hooks (PreToolUse, PostToolUse, SessionStart,
  SessionEnd, UserPromptSubmit, Stop) with exit code control flow
- Plugin System: Custom tools, commands, and hooks via plugin manifest
- Session Forking: Snapshots, rewind, fork, and switch between branches
- Vim Motions: Normal/Insert/Command/Visual modes with keyboard navigation

New files:
- src/types/{hooks,plugin,session-fork,vim}.ts
- src/constants/{hooks,plugin,session-fork,vim}.ts
- src/services/{hooks-service,plugin-loader,plugin-service,session-fork-service}.ts
- src/stores/vim-store.ts (vanilla)
- src/tui/hooks/{useVimMode,useVimStore,useTodoStore,useThemeStore}.ts
- src/tui/components/VimStatusLine.tsx

Modified:
- src/services/agent.ts (hook integration)
- src/tools/index.ts (plugin tool registration)
- src/stores/{todo-store,theme-store}.ts (converted to vanilla)
- TUI components (updated hook imports)

docs/CHANGELOG.md

@@ -9,6 +9,38 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
+- **Hooks System**: Lifecycle hooks for extensibility
+  - 6 hook events: PreToolUse, PostToolUse, SessionStart, SessionEnd, UserPromptSubmit, Stop
+  - Exit code control flow (0=allow, 1=warn, 2=block)
+  - JSON input/output via stdin/stdout
+  - Modified arguments via `updatedInput`
+  - Global + local configuration support
+  - Configurable timeout per hook
+
+- **Plugin System**: Custom tools, commands, and hooks
+  - Plugin manifest with version and capabilities
+  - Custom tool definitions via TypeScript
+  - Custom slash commands via Markdown with frontmatter
+  - Plugin-specific hooks
+  - Global (~/.config/codetyper/plugins/) + local (.codetyper/plugins/)
+  - Dynamic tool/command registration
+
+- **Session Forking/Rewind**: Branch and time-travel session history
+  - Named snapshots at any point in conversation
+  - Rewind to any snapshot by name or index
+  - Fork branches from any snapshot
+  - Switch between forks
+  - Suggested commit messages based on session content
+  - Commands: /snapshot, /rewind, /fork, /forks, /switch
+
+- **Vim Motions**: Vim-style keyboard navigation
+  - 4 modes: Normal, Insert, Command, Visual
+  - Scroll navigation (j/k, gg/G, Ctrl+d/u)
+  - Search with highlighting (/, n/N)
+  - Command mode (:q, :w, :wq, :nohl)
+  - Mode indicator in status line
+  - Configurable via settings.json
+
 - **Home Screen**: New welcome screen with centered gradient logo
   - Displays version, provider, and model info
   - Transitions to session view on first message

docs/CONTRIBUTING.md

@@ -135,11 +135,21 @@ docs: update README with new CLI options
 src/
 ├── index.ts          # Entry point only
 ├── commands/         # CLI command implementations
+├── constants/        # Centralized constants
+├── interfaces/       # Interface definitions
 ├── providers/        # LLM provider integrations
+├── services/         # Business logic services
+│   ├── hooks-service.ts    # Lifecycle hooks
+│   ├── plugin-service.ts   # Plugin management
+│   ├── plugin-loader.ts    # Plugin discovery
+│   └── session-fork-service.ts  # Session forking
+├── stores/           # Zustand state stores
+│   └── vim-store.ts  # Vim mode state
 ├── tools/            # Agent tools (bash, read, write, edit)
 ├── tui/              # Terminal UI components
-│   └── components/   # Reusable UI components
-└── types.ts          # Shared type definitions
+│   ├── components/   # Reusable UI components
+│   └── hooks/        # React hooks (useVimMode, etc.)
+└── types/            # Type definitions
 ```
 
 ### Testing
@@ -170,11 +180,16 @@ describe('PermissionManager', () => {
 | File | Purpose |
 |------|---------|
 | `src/index.ts` | CLI entry point, command registration |
-| `src/agent.ts` | Agent loop, tool orchestration |
-| `src/permissions.ts` | Permission system |
+| `src/services/agent.ts` | Agent loop, tool orchestration |
+| `src/services/permissions.ts` | Permission system |
+| `src/services/hooks-service.ts` | Lifecycle hooks |
+| `src/services/plugin-service.ts` | Plugin management |
+| `src/services/session-fork-service.ts` | Session forking |
 | `src/commands/chat-tui.tsx` | Main TUI command |
 | `src/tui/App.tsx` | Root TUI component |
 | `src/tui/store.ts` | Zustand state management |
+| `src/stores/vim-store.ts` | Vim mode state |
+| `src/tui/hooks/useVimMode.ts` | Vim keyboard handling |
 
 ### Adding a New Provider
 
@@ -192,6 +207,28 @@ describe('PermissionManager', () => {
 4. Register in `src/tools/index.ts`
 5. Add permission handling if needed
 
+### Adding a Hook Event
+
+1. Add event type to `src/types/hooks.ts`
+2. Add constants to `src/constants/hooks.ts`
+3. Add input type for the event
+4. Implement execution in `src/services/hooks-service.ts`
+5. Call hook from appropriate location
+
+### Creating a Plugin
+
+1. Create directory in `.codetyper/plugins/{name}/`
+2. Add `plugin.json` manifest
+3. Add tools in `tools/*.ts`
+4. Add commands in `commands/*.md`
+5. Add hooks in `hooks/*.sh`
+
+### Adding Vim Bindings
+
+1. Add binding to `VIM_DEFAULT_BINDINGS` in `src/constants/vim.ts`
+2. Add action handler in `src/tui/hooks/useVimMode.ts`
+3. Update documentation
+
 ## Questions?
 
 - Open a GitHub issue for questions