core: type platform api key timestamps

apps/mcp-server/src/app.rs

@@ -1584,9 +1584,7 @@ async fn require_platform_api_key(
         return Err(StatusCode::FORBIDDEN);
     }
 
-    let used_at = OffsetDateTime::now_utc()
-        .format(&Rfc3339)
-        .map_err(|_| StatusCode::INTERNAL_SERVER_ERROR)?;
+    let used_at = OffsetDateTime::now_utc();
     state
         .registry
         .touch_platform_api_key(&api_key.api_key.workspace_id, &api_key.api_key.id, &used_at)

apps/mcp-server/src/main.rs

@@ -107,6 +107,7 @@ mod tests {
     use serde_json::{Value, json};
     use sha2::{Digest, Sha256};
     use sqlx::{Executor, postgres::PgPoolOptions};
+    use time::{OffsetDateTime, format_description::well_known::Rfc3339};
     use tokio::net::TcpListener;
     use tokio::time::sleep;
 
@@ -1546,7 +1547,7 @@ mod tests {
             prefix: secret.chars().take(16).collect(),
             scopes: scopes.to_vec(),
             status: PlatformApiKeyStatus::Active,
-            created_at: "2026-03-26T10:00:00Z".to_owned(),
+            created_at: OffsetDateTime::parse("2026-03-26T10:00:00Z", &Rfc3339).unwrap(),
             last_used_at: None,
         };