feat(mcp): make sync opt-in and address review

Opt-in (mcpSyncEnabled, default OFF; routes 403 until on). Review fixes:
- codex TOML read/validated with smol-toml: CRLF, inline tables and
  command-less tables no longer yield a duplicate [mcp_servers.x]; the new
  text is re-parsed before writing
- null-prototype tables and own-key checks; unsafe names ignored at every level
- servers switched off in their own CLI (codex/opencode/antigravity) are not copied
- only CLIs that are installed or already have a config file take part
- files receiving env/headers are left 0600; symlinked configs are written through
- one apply at a time (409), unique tmp files cleaned on failure, failed status
- routes set real HTTP status codes; api-reference section; format type single-sourced

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

package-lock.json

@@ -32,6 +32,7 @@
         "jpeg-js": "^0.4.4",
         "node-pty": "^1.1.0",
         "qrcode": "^1.5.4",
+        "smol-toml": "^1.9.0",
         "undici": "^6.28.0",
         "uuid": "^14.0.0",
         "web-push": "^3.6.7",
@@ -10114,6 +10115,18 @@
         "npm": ">= 3.0.0"
       }
     },
+    "node_modules/smol-toml": {
+      "version": "1.9.0",
+      "resolved": "https://registry.npmjs.org/smol-toml/-/smol-toml-1.9.0.tgz",
+      "integrity": "sha512-hpd+HLON7HdZXqYchMM/+LaTTbdK0AU3NngIJ4KVyWbY9bfQqdL9cD+4yf6dUoU2Ap4VsU0JkQi6FxAI1B2mXQ==",
+      "license": "BSD-3-Clause",
+      "engines": {
+        "node": ">= 18"
+      },
+      "funding": {
+        "url": "https://github.com/sponsors/cyyynthia"
+      }
+    },
     "node_modules/socks": {
       "version": "2.8.9",
       "resolved": "https://registry.npmjs.org/socks/-/socks-2.8.9.tgz",