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/constants/web-search.ts

@@ -0,0 +1,41 @@
+/**
+ * Web Search Tool Constants
+ */
+
+export const WEB_SEARCH_DEFAULTS = {
+  MAX_RESULTS: 10,
+  TIMEOUT_MS: 15000,
+  USER_AGENT:
+    "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36",
+} as const;
+
+export const WEB_SEARCH_MESSAGES = {
+  SEARCHING: (query: string) => `Searching: "${query}"`,
+  NO_RESULTS: "No results found",
+  SEARCH_ERROR: (error: string) => `Search failed: ${error}`,
+  TIMEOUT: "Search timed out",
+} as const;
+
+export const WEB_SEARCH_TITLES = {
+  SEARCHING: (query: string) => `Searching: ${query}`,
+  RESULTS: (count: number) => `Found ${count} result(s)`,
+  FAILED: "Search failed",
+  NO_RESULTS: "No results",
+} as const;
+
+export const WEB_SEARCH_DESCRIPTION = `Search the web for information.
+
+Use this tool to:
+- Find documentation
+- Look up error messages
+- Research libraries and APIs
+- Get current information not in your training data
+
+Parameters:
+- query: The search query string
+- maxResults: Maximum number of results to return (default: 5)
+
+Example:
+- Search for "TypeScript generics tutorial"
+- Search for "React useEffect cleanup function"
+- Search for "bun test framework documentation"`;