Handle budget_reached as a terminal session budget error (#59228)

## What changed

Map provider `budget_reached` errors to `SessionBudgetExceeded` for HTTP 400 responses and streaming failures. End SSE streams immediately on this error, ignoring retry headers and later completion events, and display `budget reached` in the TUI.

## Testing

Add coverage for HTTP error classification, immediate SSE termination without retries, WebSocket error delivery and subsequent request recovery, and TUI error rendering and task-state cleanup.

GitOrigin-RevId: 6a62d699cdb9cb446214cacfacd0c9ed68bf21a6

codex-rs/cli/src/doctor.rs

@@ -2515,6 +2515,7 @@ fn websocket_error_detail(err: &ApiError) -> String {
         | ApiError::ContextWindowExceeded
         | ApiError::QuotaExceeded
         | ApiError::UsageNotIncluded
+        | ApiError::SessionBudgetExceeded
         | ApiError::FlexUnavailable
         | ApiError::ServerOverloaded { .. }
         | ApiError::PolicyCapacityUnavailable { .. } => format!("handshake error: {err}"),