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/.htaccess

@@ -0,0 +1,31 @@
+# Security settings for Multi-User Transcription Server
+
+# Deny access to data directory
+<DirectoryMatch "^.*/data/.*$">
+    Require all denied
+</DirectoryMatch>
+
+# Deny access to config file directly (if accessed via URL)
+<Files "config.php">
+    Require all denied
+</Files>
+
+# Enable PHP error logging (disable display for production)
+php_flag display_errors Off
+php_flag log_errors On
+
+# Set upload limits
+php_value upload_max_filesize 1M
+php_value post_max_size 1M
+
+# Disable directory listing
+Options -Indexes
+
+# Enable compression
+<IfModule mod_deflate.c>
+    AddOutputFilterByType DEFLATE text/html text/plain text/xml text/css text/javascript application/json
+</IfModule>
+
+# Set MIME types
+AddType application/json .json
+AddType text/event-stream .php