Print warning if we skip config loading (#9611)

https://github.com/openai/codex/pull/9533 silently ignored config if
untrusted. Instead, we still load it but disable it. Maybe we shouldn't
try to parse it either...

<img width="939" height="515" alt="Screenshot 2026-01-21 at 14 56 38"
src="https://github.com/user-attachments/assets/e753cc22-dd99-4242-8ffe-7589e85bef66"
/>

codex-rs/app-server-protocol/src/protocol/v2.rs

@@ -393,6 +393,8 @@ pub struct ConfigLayer {
     pub name: ConfigLayerSource,
     pub version: String,
     pub config: JsonValue,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub disabled_reason: Option<String>,
 }
 
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq, JsonSchema, TS)]