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)

src/types/index.ts

@@ -4,6 +4,23 @@
 
 export type AgentType = "coder" | "tester" | "refactorer" | "documenter";
 
+// Re-export image types
+export type {
+  ImageMediaType,
+  ImageContent,
+  TextContent,
+  MessageContent,
+  MultimodalMessage,
+  PastedImage,
+} from "@/types/image";
+
+export {
+  isImageContent,
+  isTextContent,
+  createTextContent,
+  createImageContent,
+} from "@/types/image";
+
 export type IntentType =
   | "ask"
   | "code"