feat(voice): speak every intervention, not just critical escalations

Voice was gated to severity === 'critical', so most conflict cards were
silent. Now every intervention is spoken: priority is derived from
severity in publishHermesIntervention — critical jumps the queue,
the rest serialize so concurrent alerts don't garble each other.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LuV8W8oNYRsDWKoqK8Mkqc

backend/src/action/hermes.ts

@@ -58,7 +58,10 @@ export async function publishHermesIntervention(
   void notifyCriticalLiveConversations(collision, intervention, voiceLine).catch((err) =>
     console.warn(`[live-conversation] critical notify failed: ${(err as Error).message}`),
   );
-  if (voiceLine) await speak(room, voiceLine, { priority: 'critical' });
+  if (voiceLine)
+    await speak(room, voiceLine, {
+      priority: collision.severity === 'critical' ? 'critical' : 'normal',
+    });
 }
 
 async function hermesToken(roomName: string): Promise<string> {