feat: add Codex plugin packaging (single-plugin, metadata-only) (#83)

* feat: add Codex plugin packaging (single-plugin, metadata-only)

Adds .codex-plugin/plugin.json with a skills array listing all public
skills, plus .agents/plugins/marketplace.json for one-command install:

  codex plugin marketplace add magnus919/agent-skills
  codex plugin install magnus919

Same pattern as mattpocock/skills — one plugin, explicit skill paths,
no dist/, no curation, no duplication. Bundle-internal helpers excluded
by the shared glob. CI check mode fails if the manifest drifts.

Closes #79

AI-assisted: yes (Jasper/Hermes Agent)

* chore: trigger CI

* chore: regenerate Codex plugin manifest to include neckbeard bundle

.codex-plugin/plugin.json

@@ -0,0 +1,118 @@
+{
+  "name": "magnus919",
+  "version": "1.0.0",
+  "description": "AI agent skills — reusable workflows, protocols, and knowledge packs for agentic systems.",
+  "author": {
+    "name": "Magnus Hedemark",
+    "url": "https://github.com/magnus919"
+  },
+  "homepage": "https://github.com/magnus919/agent-skills",
+  "repository": "https://github.com/magnus919/agent-skills",
+  "license": "MIT",
+  "keywords": [
+    "agent-skills",
+    "engineering",
+    "product",
+    "research",
+    "infrastructure",
+    "methodology"
+  ],
+  "skills": [
+    "./adr-authoring",
+    "./agent-council",
+    "./agent-evals-and-observability",
+    "./agent-skills",
+    "./api-design-and-evolution",
+    "./artifact-pyramids",
+    "./autogen",
+    "./backend-engineering",
+    "./brand-designer",
+    "./c4-diagramming",
+    "./chief-of-staff-methodology",
+    "./cli-builder",
+    "./color-management",
+    "./confluence-cli",
+    "./crewai",
+    "./crowdsec",
+    "./daily-life-discovery",
+    "./data-architect",
+    "./data-engineering",
+    "./data-scientist",
+    "./de-spin",
+    "./docker-compose",
+    "./dspy",
+    "./epub",
+    "./esp32-development",
+    "./financial-modeling",
+    "./fireflies",
+    "./flaresolverr",
+    "./flaresolverr-cli",
+    "./forgejo-cli",
+    "./frontend-engineering",
+    "./ghost-cli",
+    "./github-runner",
+    "./go-to-market",
+    "./gutenberg",
+    "./haystack",
+    "./hugo-theme",
+    "./jellyfin-cli",
+    "./jira-cli",
+    "./jira-jql",
+    "./kanban-guru",
+    "./kubernetes",
+    "./langchain",
+    "./langgraph",
+    "./lastfm",
+    "./legal-strategy",
+    "./linear",
+    "./llamaindex",
+    "./mermaid-diagrams",
+    "./meshcore-packet-capture",
+    "./ml-engineering",
+    "./neckbeard",
+    "./nous-branding",
+    "./open-knowledge-format",
+    "./openlibrary-cli",
+    "./opensource-contributions",
+    "./operational-design",
+    "./org-design",
+    "./peertube",
+    "./platform-engineering",
+    "./product-design-and-ux",
+    "./product-discovery",
+    "./product-methodology",
+    "./product-strategy",
+    "./pydanticai",
+    "./qa-methodology",
+    "./raleigh",
+    "./remote-systems-administration",
+    "./research-and-vault",
+    "./research-methodology",
+    "./restic",
+    "./secure-software-engineering",
+    "./security-audit-methodology",
+    "./seo-audit",
+    "./site-reliability-engineering",
+    "./software-architecture-analysis",
+    "./spec-driven-development",
+    "./strategy-frameworks",
+    "./supabase",
+    "./systematic-debugging",
+    "./tailscale",
+    "./technical-documentation",
+    "./technology-radar",
+    "./tempest-cli",
+    "./three",
+    "./tmdb-cli",
+    "./traefik",
+    "./trakt",
+    "./transistor",
+    "./vercel-eve",
+    "./verification-methodology",
+    "./web-accessibility",
+    "./woodpecker-ci",
+    "./workflow-architect",
+    "./yc-default-alive-calculator",
+    "./yc-weekly-growth-compass"
+  ]
+}