feat(codex): add Codex native plugin manifest and fix Claude plugin.json

- Add .codex-plugin/plugin.json — Codex-native plugin manifest with
  skills reference and MCP server config pointer
- Add .codex-plugin/.mcp.json — standalone MCP server config bundle
  (github, context7, exa, memory, playwright, sequential-thinking)
- Add .codex-plugin/README.md — installation guide and server reference
- Fix .claude-plugin/plugin.json — add missing agents[] (28 explicit
  file paths per validator rules), skills[], and commands[] arrays;
  remove hooks field (auto-loaded by Claude Code v2.1+ convention)
- Add tests/plugin-manifest.test.js — 16 CI tests enforcing
  PLUGIN_SCHEMA_NOTES.md rules (no hooks, arrays throughout, explicit
  agent paths, version required, .mcp.json structural checks)
- Update package.json: add .codex-plugin/ to files[], add plugin
  manifest test to npm test chain

Refs: .claude-plugin/PLUGIN_SCHEMA_NOTES.md

package-lock.json

@@ -11,6 +11,7 @@
       "license": "MIT",
       "dependencies": {
         "@iarna/toml": "^2.2.5",
+        "ajv": "^8.18.0",
         "sql.js": "^1.14.1"
       },
       "bin": {
@@ -19,7 +20,6 @@
       },
       "devDependencies": {
         "@eslint/js": "^9.39.2",
-        "ajv": "^8.18.0",
         "c8": "^10.1.2",
         "eslint": "^9.39.2",
         "globals": "^17.1.0",
@@ -449,7 +449,6 @@
       "version": "8.18.0",
       "resolved": "https://registry.npmjs.org/ajv/-/ajv-8.18.0.tgz",
       "integrity": "sha512-PlXPeEWMXMZ7sPYOHqmDyCJzcfNrUr3fGNKtezX14ykXOEIvyK81d+qydx89KY5O71FKMPaQ2vBfBFI5NHR63A==",
-      "dev": true,
       "license": "MIT",
       "dependencies": {
         "fast-deep-equal": "^3.1.3",
@@ -1043,7 +1042,6 @@
       "version": "3.1.3",
       "resolved": "https://registry.npmjs.org/fast-deep-equal/-/fast-deep-equal-3.1.3.tgz",
       "integrity": "sha512-f3qQ9oQy9j2AhBe/H9VC91wLmKBCCU/gDOnKNAYG5hswO7BLKj09Hc5HYNz9cGI++xlpDCIgDaitVs03ATR84Q==",
-      "dev": true,
       "license": "MIT"
     },
     "node_modules/fast-json-stable-stringify": {
@@ -1064,7 +1062,6 @@
       "version": "3.1.0",
       "resolved": "https://registry.npmjs.org/fast-uri/-/fast-uri-3.1.0.tgz",
       "integrity": "sha512-iPeeDKJSWf4IEOasVVrknXpaBV0IApz/gp7S2bb7Z4Lljbl2MGJRqInZiUrQwV16cpzw/D3S5j5Julj/gT52AA==",
-      "dev": true,
       "funding": [
         {
           "type": "github",
@@ -1491,7 +1488,6 @@
       "version": "1.0.0",
       "resolved": "https://registry.npmjs.org/json-schema-traverse/-/json-schema-traverse-1.0.0.tgz",
       "integrity": "sha512-NM8/P9n3XjXhIZn1lLhkFaACTOURQXjWhV4BA/RnOv8xvgqtqpAX9IO4mRQxSx1Rlo4tqzeqb0sOlruaOy3dug==",
-      "dev": true,
       "license": "MIT"
     },
     "node_modules/json-stable-stringify-without-jsonify": {
@@ -2512,7 +2508,6 @@
       "version": "2.0.2",
       "resolved": "https://registry.npmjs.org/require-from-string/-/require-from-string-2.0.2.tgz",
       "integrity": "sha512-Xf0nWe6RseziFMu+Ap9biiUbmplq6S9/p+7w7YXP/JBHhrUDDUhwa+vANyubuqfZWTveU//DYVGsDG7RKL/vEw==",
-      "dev": true,
       "license": "MIT",
       "engines": {
         "node": ">=0.10.0"