feat(observability): 管理面板可观测性接真实数据——metrics/trace/audit 三端点 + 审计持久化

- observability.go/observability_metrics.go/observability_trace.go/observability_audit.go：
  拆分保证 ≤500行/函数≤80。metrics 并发安全 MetricsCollector(方法/路径/状态计数、平均/最大延迟、
  近1s QPS窗口)；trace 并发安全 RingBuffer(默认512, newest-first)+traceSink+MultiTraceWriter；
  audit AuditStore 接口+内存回退+SQLite 持久化(NewSQLiteAuditStore 参数化 SQL+audit_logs 表)。
- server.go：Deps.AuditStore + Server.obs + 3 路由 GET /admin/observability/{metrics,trace,audit}；
  ObserveSpan/TraceSink 注入点；middleware logging recordMetric；audit 落库(仅 slog→Append)。
- 前端 Obs.tsx：metrics 接 4 张真实 StatCard+请求分布、trace 接 span 列表(展开 props/events)、
  audit 从后端拉(前端内存审计作回退)；api.ts/types.ts 加 obs 端点/类型(AdminObservabilityMetrics/
  AdminTraceSpan/AuditRecord.id 放宽)。成本指标不伪造(保留'—'+注明)。
- wire.go 收口：Deps.AuditStore 注入 gateway.NewSQLiteAuditStore(ctx, a.db)(审计真落库)，
  未注入回退内存。
- Docs/api-client.md §2/v0.6。

实机验证：三端点 200，metrics 返回 totalRequests:4/qps:4/perPath/statusCounts:{200:4}。
go build/vet/test 全绿 + 前端 tsc。trace 数据源对接(gw.TraceSink→loop tracer)因 gw/tracer
构造顺序留作可选后置(端点已就绪, 未对接 span 空)。

internal/services/gateway/observability.go

@@ -0,0 +1,125 @@
+package gateway
+
+import (
+	"net/http"
+	"strconv"
+	"time"
+
+	apperr "git.yeij.top/AskaEth/Cyrene_v2/internal/errors"
+	"git.yeij.top/AskaEth/Cyrene_v2/internal/runtime/trace"
+)
+
+// Default list limits shared by the trace/audit endpoints. Compile-time constants
+// so no magic number appears in the run path (project rule §10).
+const (
+	defaultObsLimit = 50
+	maxObsLimit     = 500
+)
+
+// observability bundles the gateway's live admin instrumentation: the request
+// metrics counter, the trace span ring buffer and the audit store. It is built in
+// New and is safe for concurrent use.
+type observability struct {
+	metrics  *MetricsCollector
+	traceBuf *RingBuffer
+	audit    AuditStore
+}
+
+// newObservability builds the instrumentation, falling back to an in-memory audit
+// store when no store is injected.
+func newObservability(deps Deps) *observability {
+	obs := &observability{
+		metrics:  newMetricsCollector(),
+		traceBuf: newRingBuffer(defaultTraceBufCap),
+	}
+	if deps.AuditStore != nil {
+		obs.audit = deps.AuditStore
+	} else {
+		obs.audit = newMemoryAuditStore()
+	}
+	return obs
+}
+
+// ObserveSpan feeds a completed trace span into the gateway's ring buffer and the
+// LLM/subagent metric counters. It is the gateway's trace injection point: the
+// composition root wires the loop tracer here (e.g. through TraceSink) so the
+// admin panel can query spans without the gateway touching wire.go.
+func (s *Server) ObserveSpan(rec trace.SpanRecord) {
+	if s.obs == nil {
+		return
+	}
+	s.obs.traceBuf.Append(rec)
+	s.obs.metrics.Observe(rec)
+}
+
+// TraceSink returns a trace.Writer that appends completed spans to the gateway's
+// trace ring buffer. Combine it with the existing JSONRecorder in the composition
+// root (e.g. trace.New(MultiTraceWriter{...})) so spans both hit stderr and the
+// admin panel.
+func (s *Server) TraceSink() trace.Writer {
+	if s.obs == nil {
+		return nil
+	}
+	return traceSink{s.obs.traceBuf}
+}
+
+// recordMetric counts one request for the observability panel.
+func (s *Server) recordMetric(method, path string, status int, durMs int64) {
+	if s.obs == nil {
+		return
+	}
+	s.obs.metrics.Record(method, path, status, durMs)
+}
+
+// adminObservabilityMetrics returns the current gateway metrics (admin read).
+func (s *Server) adminObservabilityMetrics(w http.ResponseWriter, r *http.Request) {
+	if s.obs == nil {
+		writeJSON(w, http.StatusOK, AdminMetrics{
+			PerMethod: map[string]int64{}, PerPath: map[string]int64{}, StatusCounts: map[string]int64{},
+		})
+		return
+	}
+	writeJSON(w, http.StatusOK, s.obs.metrics.Snapshot(time.Now()))
+}
+
+// adminObservabilityTrace returns the most recent traced spans (admin read).
+func (s *Server) adminObservabilityTrace(w http.ResponseWriter, r *http.Request) {
+	if s.obs == nil {
+		writeJSON(w, http.StatusOK, []AdminTraceSpan{})
+		return
+	}
+	spans := s.obs.traceBuf.Snapshot(parseLimit(r))
+	out := make([]AdminTraceSpan, 0, len(spans))
+	for _, sp := range spans {
+		out = append(out, adminSpanOf(sp))
+	}
+	writeJSON(w, http.StatusOK, out)
+}
+
+// adminObservabilityAudit returns the most recent audit entries (admin read).
+func (s *Server) adminObservabilityAudit(w http.ResponseWriter, r *http.Request) {
+	if s.obs == nil || s.obs.audit == nil {
+		writeJSON(w, http.StatusOK, []AuditRecord{})
+		return
+	}
+	records, err := s.obs.audit.List(r.Context(), parseLimit(r))
+	if err != nil {
+		s.log.Error("list audit", "err", err)
+		writeError(w, apperr.Wrap(apperr.ErrInternal, "audit_failed", "failed to list audit records"))
+		return
+	}
+	writeJSON(w, http.StatusOK, records)
+}
+
+// parseLimit parses the ?limit= query param, clamping to [1, maxObsLimit], and
+// selects defaultObsLimit when absent or invalid.
+func parseLimit(r *http.Request) int {
+	n, err := strconv.Atoi(r.URL.Query().Get("limit"))
+	if err != nil || n <= 0 {
+		return defaultObsLimit
+	}
+	if n > maxObsLimit {
+		return maxObsLimit
+	}
+	return n
+}