When a rotation fails over to a different provider/model than the preferred
(highest-weight) pick, optionally notify the client so the provider/model
change isn't silent. Opt-in via a new notify_on_failover flag, settable
globally (rotations.json top-level) or per-rotation, mirroring notifyerrors.

On a real switch (served provider/model differs from preferred), three
mechanisms carry the notice:
- Visible banner: prepended to message content (non-streaming) or a leading
  delta chunk (streaming).
- JSON metadata: an aisbf_failover object on the body / leading stream chunk.
- HTTP headers: X-AISBF-Failover/Provider/Model/Preferred-* on the
  StreamingResponse and (for non-streaming) at the rotation route.

Applied to both the normal and chunked rotation paths. The banner is injected
after caching so cache hits don't replay a stale notice; no switch means zero
overhead and nothing emitted; default off preserves existing behavior.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Streaming rotation requests returned the provider's lazy async generator to
the client before the upstream HTTP call was made, so an immediate provider
error (e.g. HTTP 400 "model not supported") surfaced mid-stream after the
200 OK headers were already sent — leaking the error to the client instead
of failing over.

- Prime streaming responses (_prime_stream) inside the rotation retry loop so
  immediate provider errors are raised within the try/except and trigger
  failover to the next provider by weight, transparently to the client.
- Add _is_non_retryable_error to skip pointless same-provider retries for
  client errors (400/401/403/404/405/422) and move straight to the next
  provider; 5xx/timeouts/network remain retryable.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Add _record_dashboard_proxy_event, _settle_market_result,
_get_market_source_details, _market_request_id and
_extract_usage_from_sse_chunk to RotationHandler, and the market
settlement cluster to AutoselectHandler. These were defined only on
RequestHandler, so rotation/autoselect requests raised AttributeError
(crash on the dashboard event path, silently swallowed elsewhere),
dropping market settlement and streaming usage capture.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

The collapsed provider-list status chip only rendered gpus[0], so a
coderai client connecting with multiple GPUs displayed just the first.
Render one chip per reported GPU (name + per-GPU VRAM), falling back to
an aggregate VRAM chip when no per-GPU detail is sent. GPU names are
HTML-escaped.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>