feat(builtin-skills): add playwright skill with MCP config and disabled_skills option

- Add playwright as builtin skill with MCP server configuration
- Add disabled_skills config option to disable specific builtin skills
- Update BuiltinSkill type to include mcpConfig field
- Update skill merger to handle mcpConfig from builtin to loaded skills
- Merge disabled_skills config and filter unavailable builtin skills at plugin init
- Update README with Built-in Skills documentation
- Regenerate JSON schema

🤖 Generated with assistance of OhMyOpenCode (https://github.com/code-yeongyu/oh-my-opencode)

assets/oh-my-opencode.schema.json

@@ -34,6 +34,15 @@
         ]
       }
     },
+    "disabled_skills": {
+      "type": "array",
+      "items": {
+        "type": "string",
+        "enum": [
+          "playwright"
+        ]
+      }
+    },
     "disabled_hooks": {
       "type": "array",
       "items": {