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>

test-server-timing.sh

@@ -0,0 +1,44 @@
+#!/bin/bash
+# Test server sync timing
+
+SERVER_URL="${1:-http://localhost:3000/api/send}"
+ROOM="${2:-test}"
+PASSPHRASE="${3:-test}"
+
+echo "Testing server sync timing..."
+echo "Server: $SERVER_URL"
+echo "Room: $ROOM"
+echo ""
+
+for i in {1..5}; do
+    START=$(date +%s%N)
+
+    RESPONSE=$(curl -s -w "\n%{http_code}\n%{time_total}" -X POST "$SERVER_URL" \
+      -H "Content-Type: application/json" \
+      -d "{
+        \"room\": \"$ROOM\",
+        \"passphrase\": \"$PASSPHRASE\",
+        \"user_name\": \"TestUser\",
+        \"text\": \"Test message $i at $(date +%H:%M:%S)\",
+        \"timestamp\": \"$(date +%H:%M:%S)\"
+      }")
+
+    HTTP_CODE=$(echo "$RESPONSE" | tail -n2 | head -n1)
+    TIME_TOTAL=$(echo "$RESPONSE" | tail -n1)
+
+    END=$(date +%s%N)
+    DURATION=$(echo "scale=0; ($END - $START) / 1000000" | bc)
+
+    if [ "$HTTP_CODE" = "200" ]; then
+        echo "✓ Message $i: ${DURATION}ms (curl reports: ${TIME_TOTAL}s)"
+    else
+        echo "✗ Message $i: HTTP $HTTP_CODE"
+        echo "$RESPONSE" | head -n1
+    fi
+
+    sleep 0.2
+done
+
+echo ""
+echo "All 5 messages sent. Check display at:"
+echo "http://localhost:3000/display?room=$ROOM"