Support enable/disable skill via config/api. (#9328)

In config.toml:
```
[[skills.config]]
path = "/Users/xl/.codex/skills/my_skill/SKILL.md"
enabled = false
```

API:
skills/list, skills/config/write

codex-rs/core/config.schema.json

@@ -75,6 +75,9 @@
         "apply_patch_freeform": {
           "type": "boolean"
         },
+        "child_agents_md": {
+          "type": "boolean"
+        },
         "collab": {
           "type": "boolean"
         },
@@ -99,9 +102,6 @@
         "experimental_windows_sandbox": {
           "type": "boolean"
         },
-        "child_agents_md": {
-          "type": "boolean"
-        },
         "include_apply_patch_tool": {
           "type": "boolean"
         },
@@ -373,6 +373,14 @@
       "description": "When set to `true`, `AgentReasoningRawContentEvent` events will be shown in the UI/output. Defaults to `false`.",
       "type": "boolean"
     },
+    "skills": {
+      "description": "User-level skill config entries keyed by SKILL.md path.",
+      "allOf": [
+        {
+          "$ref": "#/definitions/SkillsConfig"
+        }
+      ]
+    },
     "tool_output_token_limit": {
       "description": "Token budget applied when storing tool/function outputs in the context manager.",
       "type": "integer",
@@ -543,6 +551,9 @@
             "apply_patch_freeform": {
               "type": "boolean"
             },
+            "child_agents_md": {
+              "type": "boolean"
+            },
             "collab": {
               "type": "boolean"
             },
@@ -567,9 +578,6 @@
             "experimental_windows_sandbox": {
               "type": "boolean"
             },
-            "child_agents_md": {
-              "type": "boolean"
-            },
             "include_apply_patch_tool": {
               "type": "boolean"
             },
@@ -1288,6 +1296,34 @@
       },
       "additionalProperties": false
     },
+    "SkillConfig": {
+      "type": "object",
+      "required": [
+        "enabled",
+        "path"
+      ],
+      "properties": {
+        "enabled": {
+          "type": "boolean"
+        },
+        "path": {
+          "$ref": "#/definitions/AbsolutePathBuf"
+        }
+      },
+      "additionalProperties": false
+    },
+    "SkillsConfig": {
+      "type": "object",
+      "properties": {
+        "config": {
+          "type": "array",
+          "items": {
+            "$ref": "#/definitions/SkillConfig"
+          }
+        }
+      },
+      "additionalProperties": false
+    },
     "ToolsToml": {
       "type": "object",
       "properties": {