feat: integrate iCloud hide my email generation into OAuth flow

- 合并 PR #72 的核心改动：新增 iCloud Hide My Email 生成、alias 管理与成功后自动标记/删除流程
- 本地补充修复：解决与 Cloudflare Temp Email 分支差异的冲突，并补齐合并后的测试常量
- 影响范围：background 邮箱生成与 Step 9 收尾、sidepanel alias 管理 UI、manifest/rules 与新增 iCloud 测试

manifest.json

@@ -8,17 +8,29 @@
     "alarms",
     "tabs",
     "webNavigation",
+    "declarativeNetRequest",
     "debugger",
     "storage",
     "scripting",
     "activeTab"
   ],
   "host_permissions": [
+    "https://*.icloud.com/*",
+    "https://*.icloud.com.cn/*",
     "<all_urls>"
   ],
   "background": {
     "service_worker": "background.js"
   },
+  "declarative_net_request": {
+    "rule_resources": [
+      {
+        "id": "icloud_headers",
+        "enabled": true,
+        "path": "rules.json"
+      }
+    ]
+  },
   "side_panel": {
     "default_path": "sidepanel/sidepanel.html"
   },