Extend rate limit reads with usage capabilities (#42358)

## What changed

- Accept optional `account/rateLimits/read` capabilities for Luna Reserve support
  and lightweight background polling while preserving omitted and `null` params.
- Forward the Luna Reserve capability only for eligible ChatGPT sessions, and let
  lightweight polls skip the separate reset-credit detail request.
- Return the backend's `ordinaryUsageAllowed` decision only when its account and
  user identity match the active session.

## Testing

- Cover capability defaults, eligible and restricted authentication modes,
  lightweight polling, identity filtering, and backend permission handling.

GitOrigin-RevId: f407a3ae1e70e411fdf245f072a16e453f59cd87

codex-rs/app-server-protocol/schema/json/v2/GetAccountRateLimitsResponse.json

@@ -284,6 +284,13 @@
         "null"
       ]
     },
+    "ordinaryUsageAllowed": {
+      "description": "Backend permission for ordinary included usage, validated against the active account. Null means unavailable; clients must not infer recovery from percentages or reset times.",
+      "type": [
+        "boolean",
+        "null"
+      ]
+    },
     "rateLimitResetCredits": {
       "anyOf": [
         {