feat: Add timezone support with EST default

- Add TIMEZONE config option (default: America/New_York)
- Set PHP default timezone from config
- Add timezone offset and abbreviation for JavaScript
- Update stat card filters to use server timezone
- Add timezone config to Dashboard and Ticket views

Timezone can be changed via TIMEZONE env variable.
All dates now consistent with server timezone (EST by default).

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

config/config.php

@@ -65,6 +65,20 @@ $GLOBALS['config'] = [
     'RATE_LIMIT_API' => 60, // Requests per minute for API
 
     // Audit log settings
-    'AUDIT_LOG_RETENTION_DAYS' => 90
+    'AUDIT_LOG_RETENTION_DAYS' => 90,
+
+    // Timezone settings
+    // Default: America/New_York (EST/EDT)
+    // Common options: America/Chicago (CST), America/Denver (MST), America/Los_Angeles (PST), UTC
+    'TIMEZONE' => $envVars['TIMEZONE'] ?? 'America/New_York',
+    'TIMEZONE_OFFSET' => null // Will be calculated below
 ];
+
+// Set PHP default timezone
+date_default_timezone_set($GLOBALS['config']['TIMEZONE']);
+
+// Calculate UTC offset for JavaScript (in minutes, negative for west of UTC)
+$now = new DateTime('now', new DateTimeZone($GLOBALS['config']['TIMEZONE']));
+$GLOBALS['config']['TIMEZONE_OFFSET'] = $now->getOffset() / 60; // Convert seconds to minutes
+$GLOBALS['config']['TIMEZONE_ABBREV'] = $now->format('T'); // e.g., "EST", "EDT"
 ?>