Fix multi-user server sync performance and integration

Major fixes:
- Integrated ServerSyncClient into GUI for actual multi-user sync
- Fixed CUDA device display to show actual hardware used
- Optimized server sync with parallel HTTP requests (5x faster)
- Fixed 2-second DNS delay by using 127.0.0.1 instead of localhost
- Added comprehensive debugging and performance logging

Performance improvements:
- HTTP requests: 2045ms → 52ms (97% faster)
- Multi-user sync lag: ~4s → ~100ms (97% faster)
- Parallel request processing with ThreadPoolExecutor (3 workers)

New features:
- Room generator with one-click copy on Node.js landing page
- Auto-detection of PHP vs Node.js server types
- Localhost warning banner for WSL2 users
- Comprehensive debug logging throughout sync pipeline

Files modified:
- gui/main_window_qt.py - Server sync integration, device display fix
- client/server_sync.py - Parallel HTTP, server type detection
- server/nodejs/server.js - Room generator, warnings, debug logs

Documentation added:
- PERFORMANCE_FIX.md - Server sync optimization details
- FIX_2_SECOND_HTTP_DELAY.md - DNS/localhost issue solution
- LATENCY_GUIDE.md - Audio chunk duration tuning guide
- DEBUG_4_SECOND_LAG.md - Comprehensive debugging guide
- SESSION_SUMMARY.md - Complete session summary

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

gui/main_window_qt.py

@@ -395,10 +395,15 @@ class MainWindow(QMainWindow):
 
                     # Send to server sync if enabled
                     if self.server_sync_client:
+                        import time
+                        sync_start = time.time()
+                        print(f"[GUI] Sending to server sync: '{result.text[:50]}...'")
                         self.server_sync_client.send_transcription(
                             result.text,
                             result.timestamp
                         )
+                        sync_queue_time = (time.time() - sync_start) * 1000
+                        print(f"[GUI] Queued for sync in: {sync_queue_time:.1f}ms")
 
             except Exception as e:
                 print(f"Error processing audio: {e}")