Add multi-user server sync (PHP server + client)

Phase 2 implementation: Multiple streamers can now merge their captions
into a single stream using a PHP server.

PHP Server (server/php/):
- server.php: API endpoint for sending/streaming transcriptions
- display.php: Web page for viewing merged captions in OBS
- config.php: Server configuration
- .htaccess: Security settings
- README.md: Comprehensive deployment guide

Features:
- Room-based isolation (multiple groups on same server)
- Passphrase authentication per room
- Real-time streaming via Server-Sent Events (SSE)
- Different colors for each user
- File-based storage (no database required)
- Auto-cleanup of old rooms
- Works on standard PHP hosting

Client-Side:
- client/server_sync.py: HTTP client for sending to PHP server
- Settings dialog updated with server sync options
- Config updated with server_sync section

Server Configuration:
- URL: Server endpoint (e.g., http://example.com/transcription/server.php)
- Room: Unique room name for your group
- Passphrase: Shared secret for authentication

OBS Integration:
Display URL format:
http://example.com/transcription/display.php?room=ROOM&passphrase=PASS&fade=10&timestamps=true

NOTE: Main window integration pending (client sends transcriptions)

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

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

server/php/config.php

@@ -0,0 +1,42 @@
+<?php
+/**
+ * Multi-User Transcription Server - Configuration
+ *
+ * Simple PHP server for merging transcriptions from multiple clients
+ */
+
+// Session configuration
+define('SESSION_LIFETIME', 3600); // 1 hour
+define('MAX_TRANSCRIPTIONS_PER_ROOM', 100);
+
+// Storage directory (must be writable by PHP)
+define('STORAGE_DIR', __DIR__ . '/data');
+
+// Enable CORS for cross-origin requests (if needed)
+define('ENABLE_CORS', true);
+
+// Cleanup old sessions older than this (seconds)
+define('CLEANUP_THRESHOLD', 7200); // 2 hours
+
+// Initialize storage directory
+if (!file_exists(STORAGE_DIR)) {
+    mkdir(STORAGE_DIR, 0755, true);
+}
+
+// Security headers
+header('X-Content-Type-Options: nosniff');
+header('X-Frame-Options: SAMEORIGIN');
+
+// CORS headers (if enabled)
+if (ENABLE_CORS) {
+    header('Access-Control-Allow-Origin: *');
+    header('Access-Control-Allow-Methods: GET, POST, OPTIONS');
+    header('Access-Control-Allow-Headers: Content-Type');
+}
+
+// Handle preflight requests
+if ($_SERVER['REQUEST_METHOD'] === 'OPTIONS') {
+    http_response_code(200);
+    exit();
+}
+?>