Show native dollar thread usage for ENT26 plans (#57251)

## Why

ENT26 plans are billed directly in dollars, so credit estimates and credit-weighted breakdowns do not describe their thread usage.

## What changed

- Expose optional `nativeUsageUsdMicros` in app-server `ThreadUsage` responses and generated schemas and SDK types. Missing native usage means unknown, not zero.
- Enable ENT26 usage fetching and display native dollar amounts in `/status`, the status line, terminal titles, and the agents overview. Hide credits and omit credit-weighted `/status` breakdowns for these plans.
- Use native dollar amounts when tracking post-turn usage settlement for ENT26 plans.

## Testing

Add coverage for native usage forwarding, ENT26 billing displays, and settlement polling with stale, missing, or zero dollar amounts.

GitOrigin-RevId: ca8ea98141a66bdf0a27feb9f58f67822b821f5f

sdk/python/src/openai_codex/generated/v2_all.py

@@ -10784,6 +10784,13 @@ class ThreadUsage(BaseModel):
     estimated_usage_credits_micros: Annotated[int, Field(alias="estimatedUsageCreditsMicros")]
     estimated_usage_usd_micros: Annotated[int | None, Field(alias="estimatedUsageUsdMicros")] = None
     groups: list[ThreadUsageBreakdownGroup]
+    native_usage_usd_micros: Annotated[
+        int | None,
+        Field(
+            alias="nativeUsageUsdMicros",
+            description="Native dollar usage, independent of credit estimates. None means unknown, not zero.",
+        ),
+    ] = None
     thread_id: Annotated[str, Field(alias="threadId")]