docs(observability): document phase-0 telemetry and baseline workflow

docs/architecture/AGENT_DIAGRAM.md

@@ -27,6 +27,7 @@ flowchart LR
   subgraph HOST[Host (Flynn Daemon)]
     CA[ChannelAdapters]
     GW[Gateway\nHTTP + WS JSON-RPC + Web UI]
+    MC[MetricsCollector\nrun state + cancel latency + reactions]
     RT[Routing\ncreateMessageRouter()]
     PF[Preferences\n~/.local/share/flynn/preferences.json\nmodelTier + backendMode]
     SM[SessionManager\nSQLite]
@@ -60,6 +61,7 @@ flowchart LR
 
   CH --> CA
   GW --> RT
+  GW --> MC
   CA --> RT
   RT --> SM
   RT --> OR
@@ -147,6 +149,7 @@ Key files:
 - Model routing: `src/models/router.ts`
 - Tool policy + execution: `src/tools/policy.ts`, `src/tools/executor.ts`
 - Canary backend telemetry summarization (offline evaluation): `src/audit/backendCanarySummary.ts`, `scripts/summarize-backend-canary.ts`
+- Phase 0 baseline telemetry summarization: `src/audit/phase0BaselineSummary.ts`, `scripts/summarize-phase0-baseline.ts`
 
 ## Component Graph (Agent-Safety Boundary)