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/popup/Popup.tsx

@@ -1,41 +1,6 @@
 import React, { useEffect, useRef, useState } from 'react';
 import { createRoot } from 'react-dom/client';
-
-// ─── Safe chrome storage wrapper ─────────────────────────────────────────────
-
-function safeStorageGet(
-  storage: chrome.storage.StorageArea,
-  keys: string[],
-  callback: (result: Record<string, string>) => void,
-) {
-  try {
-    if (typeof chrome === 'undefined' || !chrome.runtime?.id) return;
-    storage.get(keys, callback);
-  } catch (err) {
-    console.warn('LexAI: Extension context invalidated', err);
-  }
-}
-
-function safeStorageSet(storage: chrome.storage.StorageArea, data: Record<string, string>) {
-  try {
-    if (typeof chrome === 'undefined' || !chrome.runtime?.id) return;
-    storage.set(data);
-  } catch (err) {
-    console.warn('LexAI: Extension context invalidated', err);
-  }
-}
-
-async function safeSendMessage(
-  message: Record<string, unknown>,
-): Promise<Record<string, string> | null> {
-  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;
-  }
-}
+import { safeSendMessage, safeStorageGet, safeStorageSet } from '@lib/messaging';
 
 // ─── Constants ───────────────────────────────────────────────────────────────
 
@@ -222,7 +187,7 @@ function Popup() {
 
   // Load config + restore session input + load writing style
   useEffect(() => {
-    safeStorageGet(chrome.storage.local, ['provider', 'apiKey', 'apiKeyEnc', 'model', 'writingStyle'], (result) => {
+    safeStorageGet(['provider', 'apiKey', 'apiKeyEnc', 'model', 'writingStyle'], (result) => {
       if (result.apiKey || result.apiKeyEnc) {
         setConfigured(true);
         setProvider(result.provider || 'openai');
@@ -235,11 +200,11 @@ function Popup() {
 
     if (!sessionRestored.current) {
       sessionRestored.current = true;
-      safeStorageGet(chrome.storage.session, ['lexai_popup_input'], (res) => {
+      safeStorageGet(['lexai_popup_input'], (res) => {
         if (res.lexai_popup_input) {
           setInputText(res.lexai_popup_input);
         }
-      });
+      }, chrome.storage.session);
     }
   }, []);
 
@@ -247,14 +212,14 @@ function Popup() {
   const handleInputChange = (e: React.ChangeEvent<HTMLTextAreaElement>) => {
     const val = e.target.value;
     setInputText(val);
-    safeStorageSet(chrome.storage.session, { lexai_popup_input: val });
+    safeStorageSet({ lexai_popup_input: val }, undefined, chrome.storage.session);
   };
 
   // Save writing style on change
   const handleStyleChange = (e: React.ChangeEvent<HTMLSelectElement>) => {
     const val = e.target.value;
     setWritingStyle(val);
-    safeStorageSet(chrome.storage.local, { writingStyle: val });
+    safeStorageSet({ writingStyle: val });
   };
 
   const openSettings = () => {