feat: add Codex CLI plugin manifest (#350)

Add Codex plugin support for discovery via codex-plugin-scanner:
- .codex-plugin/plugin.json — plugin manifest
- .mcp.json — MCP server config (starts server_fastmcp)
- skills/skill-seekers/SKILL.md — bundled skill for Codex
- .gitignore — allow root .mcp.json to be tracked

Co-authored-by: internet-dot <28622406+internet-dot@users.noreply.github.com>
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.codex-plugin/plugin.json

@@ -0,0 +1,21 @@
+{
+  "name": "skill-seekers",
+  "version": "3.5.0",
+  "description": "Convert docs and repos into AI skills via MCP",
+  "author": {
+    "name": "yusufkaraaslan",
+    "url": "https://github.com/yusufkaraaslan/Skill_Seekers"
+  },
+  "homepage": "https://skillseekersweb.com/",
+  "repository": "https://github.com/yusufkaraaslan/Skill_Seekers",
+  "keywords": ["mcp", "codex", "skills", "documentation"],
+  "mcpServers": "./.mcp.json",
+  "skills": "./skills/",
+  "interface": {
+    "displayName": "Skill Seekers",
+    "shortDescription": "Convert docs and repos into AI skills via MCP",
+    "longDescription": "Convert documentation websites, GitHub repositories, and PDFs into AI skills with automatic conflict detection.",
+    "category": "Development",
+    "websiteURL": "https://skillseekersweb.com/"
+  }
+}