fix(registry): retry failed startup discovery once in the background

A provider whose discovery failed during the warm fill at pod start
went without discovered models for a full discovery interval, which is
1 hour by default. It also stayed that way until a request arrived
after the interval. Production logs showed this for openai-audio and
anthropic when outbound calls were slow at startup.

A provider that fails the warm fill now gets one background retry
after 10s. The retry has its own timeout and uses the same refresh
bookkeeping. It is skipped when a refresh is already in flight or has
finished since the warm fill, and it is not scheduled when the parent
context was canceled. A recovery logs one INFO line. If the retry also
fails, the existing breaker behaviour applies unchanged.

The retry delay and the warm-fill timeout can be set per registry for
tests. yaegi-check probes the retry under the interpreter.

Claude-Session: https://claude.ai/code/session_01V5jYJNxpDFdJkyyExpADrv

llmgateway.go

@@ -1146,6 +1146,10 @@ func newGateway(ctx context.Context, next http.Handler, config *Config, name str
 	// Routes the self-resolving conditions (a model id two providers both
 	// serve) to WARN instead of ERROR — see the registry's warn field.
 	registry.warn = g.warnf
+	// Routes retryWarmFill's "recovered after retry" success line to INFO
+	// instead of the constructor's default ERROR (g.errorf, passed to
+	// newModelRegistry above) — see the registry's info field doc comment.
+	registry.info = g.logf
 	// ctx is passed through unwrapped, not re-bounded to warmFillTimeout here:
 	// warmFill already gives each discovery-enabled provider its own fresh
 	// warmFillTimeout budget per provider (registry.go). Wrapping ctx to a