feat: purge legacy agent hosts and land vault Chrome extension path

Retire ACP/Hermes/OpenCode surfaces and rename hermes_tools to
mnote_agent_tools so Page AI stays on Pi Lab only. Add Chrome vault
extension + extension token route, pre-release purge design, and soft-retire
legacy smokes for the small-group production cut.

extensions/mnote-vault/manifest.json

@@ -0,0 +1,49 @@
+{
+  "manifest_version": 3,
+  "name": "MNote Vault",
+  "version": "0.2.3",
+  "description": "将外站登录/注册账号与浏览器登录态保存到 MNote 密码箱（提交缓存 → 登录后确认；每账号独立 session 文件）。",
+  "permissions": [
+    "storage",
+    "activeTab",
+    "scripting",
+    "alarms",
+    "cookies",
+    "tabs"
+  ],
+  "optional_host_permissions": [
+    "http://*/*",
+    "https://*/*"
+  ],
+  "host_permissions": [
+    "http://*/*",
+    "https://*/*"
+  ],
+  "background": {
+    "service_worker": "background.js",
+    "type": "module"
+  },
+  "action": {
+    "default_popup": "popup.html",
+    "default_title": "MNote Vault",
+    "default_icon": {
+      "16": "icons/icon16.png",
+      "48": "icons/icon48.png",
+      "128": "icons/icon128.png"
+    }
+  },
+  "options_page": "options.html",
+  "icons": {
+    "16": "icons/icon16.png",
+    "48": "icons/icon48.png",
+    "128": "icons/icon128.png"
+  },
+  "content_scripts": [
+    {
+      "matches": ["http://*/*", "https://*/*"],
+      "js": ["content.js"],
+      "run_at": "document_idle",
+      "all_frames": false
+    }
+  ]
+}