feat: multi-provider support — Anthropic + Ollama (P2-002) (#74)

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

apps/gateway/src/chat/chat.gateway.ts

@@ -17,6 +17,8 @@ import { v4 as uuid } from 'uuid';
 interface ChatMessage {
   conversationId?: string;
   content: string;
+  provider?: string;
+  modelId?: string;
 }
 
 @WebSocketGateway({
@@ -65,7 +67,10 @@ export class ChatGateway implements OnGatewayInit, OnGatewayConnection, OnGatewa
     try {
       let agentSession = this.agentService.getSession(conversationId);
       if (!agentSession) {
-        agentSession = await this.agentService.createSession(conversationId);
+        agentSession = await this.agentService.createSession(conversationId, {
+          provider: data.provider,
+          modelId: data.modelId,
+        });
       }
     } catch (err) {
       this.logger.error(