feat: Phase 2 - reliability & observability

- Circuit breaker: proper thresholds (3 failures, 30s timeout)
- HTTP timeouts: 30s on all providers (was no timeout)
- Structured logging: slog replaces fmt.Printf throughout
- Stream errors: propagated as SSE error events to client
- Registry fetch: retry with backoff (3 attempts)
- Registry reads in dashboard protected by RWMutex

internal/providers/grok.go

@@ -2,6 +2,7 @@ package providers
 
 import (
 	"context"
+	"time"
 	"encoding/json"
 	"fmt"
 
@@ -18,7 +19,7 @@ type GrokProvider struct {
 
 func NewGrokProvider(cfg config.GrokConfig, apiKey string) *GrokProvider {
 	return &GrokProvider{
-		client: resty.New(),
+		client: resty.New().SetTimeout(30 * time.Second),
 		config: cfg,
 		apiKey: apiKey,
 	}