fix: resolve 6 remaining defects (P2-18, P2-21, P3-04, P3-05, P3-06, P3-02)

- P2-18: TOTP QR code local generation via qrcode lib (no external service)
- P2-21: Suspend foreign LLM providers (OpenAI/Anthropic/Gemini) for early stage
- P3-04: get_progress() now calculates actual percentage from completed/total steps
- P3-05: saveSaaSSession calls now have .catch() error logging
- P3-06: SaaS relay chatStream passes session_key/agent_id to backend
- P3-02: Whiteboard unification plan document created

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

desktop/src/lib/saas-relay-client.ts

@@ -119,6 +119,9 @@ export function createSaaSRelayGatewayClient(
         stream: true,
       };
 
+      // P3-06: Pass sessionKey/agentId to relay for session continuity
+      if (opts?.sessionKey) body['session_key'] = opts.sessionKey;
+      if (opts?.agentId) body['agent_id'] = opts.agentId;
       if (opts?.thinking_enabled) body['thinking_enabled'] = true;
       if (opts?.reasoning_effort) body['reasoning_effort'] = opts.reasoning_effort;