…ints

Add an OpenAI-compatible API surface to the gateway so that standard
OpenAI client libraries can interact with ZeroClaw directly.

Endpoints:
- POST /v1/chat/completions — supports both streaming (SSE) and
  non-streaming responses, bearer token auth, rate limiting
- GET /v1/models — returns the gateway's configured model

The chat completions endpoint accepts the standard OpenAI request format
(model, messages, temperature, stream) and returns responses in the
OpenAI envelope format. Streaming uses SSE with delta chunks and a
[DONE] sentinel. A 512KB body limit is applied (vs 64KB default) since
chat histories can be large.

When the underlying provider doesn't support native streaming, the
handler falls back to wrapping the non-streaming response in a single
SSE chunk for transparent compatibility.

Includes 8 unit tests for request/response serialization.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Implement the streaming provider trait methods for Bedrock, enabling
real-time token-by-token responses via the ConverseStream endpoint.

Key implementation details:
- Uses /model/{id}/converse-stream endpoint with SigV4 signing
- Parses AWS binary event-stream format (application/vnd.amazon.eventstream)
  with a minimal parser (~60 lines) — no new crate dependencies needed
- Handles contentBlockDelta events for text extraction, plus error and
  exception events
- Uses mpsc channel + stream::unfold pattern (matching compatible.rs)
- Clones credentials for async task ownership

The binary event-stream parser extracts frame lengths, header sections
(looking for :event-type), and payload bytes. CRC validation is skipped
since TLS already provides integrity guarantees.

Includes 10 new tests for URL formatting, binary parsing, and
deserialization.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>