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

.claude-plugin/plugin.json

@@ -21,5 +21,37 @@
     "workflow",
     "automation",
     "best-practices"
-  ]
+  ],
+  "agents": [
+    "./agents/architect.md",
+    "./agents/build-error-resolver.md",
+    "./agents/chief-of-staff.md",
+    "./agents/code-reviewer.md",
+    "./agents/cpp-build-resolver.md",
+    "./agents/cpp-reviewer.md",
+    "./agents/database-reviewer.md",
+    "./agents/doc-updater.md",
+    "./agents/docs-lookup.md",
+    "./agents/e2e-runner.md",
+    "./agents/flutter-reviewer.md",
+    "./agents/go-build-resolver.md",
+    "./agents/go-reviewer.md",
+    "./agents/harness-optimizer.md",
+    "./agents/java-build-resolver.md",
+    "./agents/java-reviewer.md",
+    "./agents/kotlin-build-resolver.md",
+    "./agents/kotlin-reviewer.md",
+    "./agents/loop-operator.md",
+    "./agents/planner.md",
+    "./agents/python-reviewer.md",
+    "./agents/pytorch-build-resolver.md",
+    "./agents/refactor-cleaner.md",
+    "./agents/rust-build-resolver.md",
+    "./agents/rust-reviewer.md",
+    "./agents/security-reviewer.md",
+    "./agents/tdd-guide.md",
+    "./agents/typescript-reviewer.md"
+  ],
+  "skills": ["./skills/"],
+  "commands": ["./commands/"]
 }