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

.gitignore

@@ -1,13 +1,16 @@
-.env
-.env.*
-!.env.example
-/target
-/llm-proxy
-/llm-proxy-go
-/gophergate
 /data/
 *.db
 *.db-shm
 *.db-wal
+.env
+.env.*
+!.env.example
+/gophergate
+/llm-proxy
+/llm-proxy-go
 *.log
+.opencode/
+.pi-lens/
+.pi-lens/cache/
 server.pid
+/target