aibridge: Display interception failures in the AI Bridge UI #1393

Description

When an upstream provider rejects a request, the interception is recorded but contains no useful information: 0 tokens, 0 tool calls, no error message. This makes failed requests indistinguishable from successful ones in the UI.

When the upstream fails, the error is logged and tracked in metrics but not stored on the interception record itself.

We should distinguish between:

• Unrecoverable errors (4xx — e.g., 400 Bad Request, 403 Forbidden): these indicate a client or configuration issue that won't resolve on its own.
• Recoverable errors (e.g., 5xx, 429 Rate Limit): these are transient and may succeed on retry.

Open Questions

• Should we store the upstream error response (status code, message) on the interception record?
• How should the UI display each error type?
• In a multi-turn conversation, individual requests may fail while others succeed. How do we show this without cluttering the view?