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/app-server-protocol/src/protocol/common.rs

@@ -133,6 +133,10 @@ client_request_definitions! {
         params: v2::SkillsListParams,
         response: v2::SkillsListResponse,
     },
+    SkillsConfigWrite => "skills/config/write" {
+        params: v2::SkillsConfigWriteParams,
+        response: v2::SkillsConfigWriteResponse,
+    },
     TurnStart => "turn/start" {
         params: v2::TurnStartParams,
         response: v2::TurnStartResponse,