Treat model-not-found provider errors as terminal failures (#56445)

## Why

Provider errors with code `model_not_found` should end the turn immediately and preserve the provider's message instead of triggering retries.

## What changed

- Recognize `model_not_found` in HTTP 400, 403, and 404 responses and in streamed `error` and `response.failed` events.
- Preserve the provider message and any available HTTP status, and expose `modelNotFound` through the app-server protocol and generated schemas and SDK types.

## Testing

Add coverage for HTTP classification, statusless stream errors, and terminal failures without retries across HTTP, SSE, and WebSocket responses. Verify that `thread/read` preserves the error reported by the live notification.

GitOrigin-RevId: 88f824ac03c8c9669915b1e40c67b76c08326fbe

codex-rs/response-debug-context/src/lib.rs

@@ -85,6 +85,7 @@ pub fn telemetry_api_error_message(error: &ApiError) -> String {
         ApiError::Retryable { .. } => "retryable error".to_string(),
         ApiError::RateLimitExceeded { .. } => "rate limit exceeded".to_string(),
         ApiError::RateLimit(_) => "rate limit".to_string(),
+        ApiError::ModelNotFound { .. } => "model not found".to_string(),
         ApiError::InvalidRequest { .. } | ApiError::InvalidPrompt { .. } => {
             "invalid request".to_string()
         }