feat(plugins): Codex plugin support + Python plugin variant for Claude

- Add 1c-skills-py to .claude-plugin/marketplace.json (→ port-claude-code-py)
- New .agents/plugins/marketplace.json — Codex marketplace with PS + Py plugins
- Templates .github/templates/{codex,claude}-plugin.json.tmpl rendered by CI
- build-ports.yml: generate plugin manifests on port-codex/port-codex-py/port-claude-code-py; Codex version YYYY.M.D+sha7 auto-bumped per push
- README: install instructions for Codex + Py variant for Claude
- .gitignore: narrow .agents/ → .agents/skills/ so the marketplace is tracked

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.agents/plugins/marketplace.json

@@ -0,0 +1,40 @@
+{
+  "name": "cc-1c-skills",
+  "interface": {
+    "displayName": "1C Skills"
+  },
+  "plugins": [
+    {
+      "name": "1c-skills",
+      "source": {
+        "source": "url",
+        "url": "https://github.com/Nikolay-Shirokov/cc-1c-skills.git",
+        "ref": "port-codex"
+      },
+      "policy": {
+        "installation": "AVAILABLE",
+        "authentication": "OFF"
+      },
+      "category": "Development",
+      "interface": {
+        "shortDescription": "PowerShell runtime (Windows-first)"
+      }
+    },
+    {
+      "name": "1c-skills-py",
+      "source": {
+        "source": "url",
+        "url": "https://github.com/Nikolay-Shirokov/cc-1c-skills.git",
+        "ref": "port-codex-py"
+      },
+      "policy": {
+        "installation": "AVAILABLE",
+        "authentication": "OFF"
+      },
+      "category": "Development",
+      "interface": {
+        "shortDescription": "Python runtime (Linux/Mac/Windows)"
+      }
+    }
+  ]
+}