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/.htaccess

@@ -1,22 +1,15 @@
 # Security settings for Multi-User Transcription Server
-
-# Deny access to data directory
-<DirectoryMatch "^.*/data/.*$">
-    Require all denied
-</DirectoryMatch>
+# Compatible with both mod_php and php-fpm
 
 # 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
+# Deny access to .json data files
+<FilesMatch "\.json$">
+    Require all denied
+</FilesMatch>
 
 # Disable directory listing
 Options -Indexes
@@ -29,3 +22,7 @@ Options -Indexes
 # Set MIME types
 AddType application/json .json
 AddType text/event-stream .php
+
+# NOTE: PHP settings (display_errors, upload limits) must be configured in:
+# - For php-fpm: /etc/php/X.X/fpm/pool.d/www.conf or php.ini
+# - For mod_php: Can use php_flag/php_value directives here