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

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

@@ -1,3 +1,5 @@
+//! Thread billing amounts, keeping native dollars separate from credit estimates.
+
 use crate::JsonSchema;
 use crate::TS;
 use serde::Deserialize;
@@ -10,6 +12,9 @@ pub struct ThreadUsage {
     pub thread_id: String,
     pub estimated_usage_credits_micros: i64,
     pub estimated_usage_usd_micros: Option<i64>,
+    /// Native dollar usage, independent of credit estimates. None means unknown, not zero.
+    #[ts(optional, as = "Option<Option<i64>>")]
+    pub native_usage_usd_micros: Option<i64>,
     pub groups: Vec<ThreadUsageBreakdownGroup>,
 }