refactor: extract shared types + safe chrome wrappers into src/lib

- src/lib/types.ts: message contract (both ANALYZE_TEXT shapes preserved),
  config/response types, storage-key constants.
- src/lib/messaging.ts: single safeStorageGet/safeStorageSet/safeSendMessage/
  isExtensionValid implementation replacing the three divergent copies in
  Options, Popup, and content. Content script keeps its refresh-toast
  behavior via an onContextInvalidated callback.
- New '@lib' import alias (wxt force-overwrites '~' and '@' to srcDir, so
  those cannot point at ./src); wired in wxt.config, tsconfig, vitest.
- tests/unit/messaging.test.ts: 14 unit tests over the wrappers.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

entrypoints/options/Options.tsx

@@ -1,6 +1,7 @@
 import React, { useEffect, useRef, useState } from 'react';
 import { createRoot } from 'react-dom/client';
 import nacl from 'tweetnacl';
+import { safeSendMessage, safeStorageGet, safeStorageSet } from '@lib/messaging';
 
 // ─── Provider config ──────────────────────────────────────────────────────────
 
@@ -166,40 +167,6 @@ const styles = {
   } as React.CSSProperties,
 };
 
-// ─── Safe chrome storage wrappers ────────────────────────────────────────────
-
-function safeStorageGet(keys: string[], callback: (result: Record<string, string>) => void) {
-  try {
-    if (typeof chrome === 'undefined' || !chrome.runtime?.id) return;
-    chrome.storage.local.get(keys, callback);
-  } catch (err) {
-    console.warn('LexAI: Extension context invalidated', err);
-  }
-}
-
-function safeStorageSet(data: Record<string, string>, callback?: () => void) {
-  try {
-    if (typeof chrome === 'undefined' || !chrome.runtime?.id) return;
-    if (callback) {
-      chrome.storage.local.set(data, callback);
-    } else {
-      chrome.storage.local.set(data);
-    }
-  } catch (err) {
-    console.warn('LexAI: Extension context invalidated', err);
-  }
-}
-
-async function safeSendMessage(message: Record<string, unknown>): Promise<any> {
-  try {
-    if (typeof chrome === 'undefined' || !chrome.runtime?.id) return null;
-    return await chrome.runtime.sendMessage(message);
-  } catch (err) {
-    console.warn('LexAI: sendMessage failed', err);
-    return null;
-  }
-}
-
 // ─── Component ────────────────────────────────────────────────────────────────
 
 function OptionsPage() {