feat(M5-004,M5-005,M5-006,M5-007): session-conversation binding, session:info broadcast, agent creation from TUI, and session metrics (#321)

Co-authored-by: Jason Woltje <jason@diversecanvas.com>
Co-committed-by: Jason Woltje <jason@diversecanvas.com>

apps/gateway/src/agent/session.dto.ts

@@ -1,11 +1,32 @@
+/** Token usage metrics for a session (M5-007). */
+export interface SessionTokenMetrics {
+  input: number;
+  output: number;
+  cacheRead: number;
+  cacheWrite: number;
+  total: number;
+}
+
+/** Per-session metrics tracked throughout the session lifetime (M5-007). */
+export interface SessionMetrics {
+  tokens: SessionTokenMetrics;
+  modelSwitches: number;
+  messageCount: number;
+  lastActivityAt: string;
+}
+
 export interface SessionInfoDto {
   id: string;
   provider: string;
   modelId: string;
+  /** M5-005: human-readable agent name when an agent config is applied. */
+  agentName?: string;
   createdAt: string;
   promptCount: number;
   channels: string[];
   durationMs: number;
+  /** M5-007: per-session metrics (token usage, model switches, etc.) */
+  metrics: SessionMetrics;
 }
 
 export interface SessionListDto {