Fix PHP-FPM compatibility and add server diagnostics

Changes to .htaccess:
- Removed php_flag and php_value directives (don't work with php-fpm)
- Simplified DirectoryMatch to FilesMatch for .json files
- Added note about configuring PHP settings in php.ini/pool config
- More compatible with user directories

Added diagnostic.php:
- Tests PHP version, extensions, and configuration
- Checks storage directory permissions
- Tests Server-Sent Events (SSE) connection
- Shows server API type (php-fpm vs mod_php)
- Provides troubleshooting hints for common issues
- Live SSE connection test with detailed logging

Added data/index.php:
- Blocks direct access to data directory
- Returns 403 Forbidden

Fixes:
- php-fpm environments not respecting .htaccess PHP settings
- DirectoryMatch issues in user directories
- Hard to diagnose connection problems

Usage: Navigate to diagnostic.php to troubleshoot server issues

server/php/data/index.php

@@ -0,0 +1,5 @@
+<?php
+// Block direct access to data directory
+http_response_code(403);
+header('Content-Type: text/plain');
+die('Access Denied');