feat(trace): waterfall visualization + persona YAML sync

- trace.Logger: Trace+Span model with 14+ hop tracking
- trace.SpanTimer: convenience API for instrumentation
- trace_adapter.go: serialize Trace+Span for frontend
- Frontend TracePage: colored waterfall bars, expand/collapse, detail popup
- persona.go: full v1 YAML parser (identity/traits/forbidden/sections)
- cyrene_persona.yaml: v1 persona config copied to v2
- Orchestrator: TraceHook + MemoryExtractor injection points

backend/services/gateway/api/router.go

@@ -69,6 +69,7 @@ type LLMCallLogger interface {
 // TraceLogger provides full-chain trace events.
 type TraceLogger interface {
 	Recent(n int) []map[string]any
+	Clear()    // Remove old traces
 }
 
 // PerfMonitor provides performance snapshot history.
@@ -515,10 +516,15 @@ func num(m map[string]any, key string) int {
 
 func (r *Router) traceHandler(w http.ResponseWriter, req *http.Request) {
 	if r.deps.TraceLog == nil {
-		writeJSON(w, 200, M{"events": []any{}})
+		writeJSON(w, 200, M{"traces": []any{}})
 		return
 	}
-	writeJSON(w, 200, M{"events": r.deps.TraceLog.Recent(100)})
+	if req.Method == "DELETE" {
+		r.deps.TraceLog.Clear()
+		writeJSON(w, 200, M{"ok": true})
+		return
+	}
+	writeJSON(w, 200, M{"traces": r.deps.TraceLog.Recent(50)})
 }
 
 func (r *Router) perfHandler(w http.ResponseWriter, req *http.Request) {