feat(metrics): add phase-0 baseline counters

Diagrams reviewed: docs/architecture/AGENT_DIAGRAM.md, docs/architecture/GATEWAY_SESSIONS_AND_QUEUE.md, docs/api/PROTOCOL.md (no changes required).

src/daemon/index.ts

@@ -260,6 +260,7 @@ export async function startDaemon(config: Config, options?: StartDaemonOptions):
   const messageRouter = createMessageRouter({
     sessionManager, modelRouter, systemPrompt, toolRegistry, toolExecutor,
     config, memoryStore, agentConfigRegistry, agentRouter, sandboxManager, commandRegistry, hookEngine, intentRegistry, routingPolicy, skillRegistry, skillInstaller,
+    metrics: gateway.getMetrics(),
     getBackendMode: () => backendMode,
     setBackendMode: (mode) => {
       backendMode = mode;