feat: Add 9 new features for enhanced UX and security

Quick Wins:
- Feature 1: Ticket linking in comments (#123456789 auto-links)
- Feature 6: Checkbox click area fix (click anywhere in cell)
- Feature 7: User groups display in settings modal

UI Enhancements:
- Feature 4: Collapsible sidebar with localStorage persistence
- Feature 5: Inline ticket preview popup on hover (300ms delay)
- Feature 2: Mobile responsive improvements (44px touch targets, iOS zoom fix)

Major Features:
- Feature 3: Kanban card view with status columns (toggle with localStorage)
- Feature 9: API key generation admin panel (/admin/api-keys)
- Feature 8: Ticket visibility levels (public/internal/confidential)

New files:
- views/admin/ApiKeysView.php
- api/generate_api_key.php
- api/revoke_api_key.php
- migrations/008_ticket_visibility.sql

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

api/revoke_api_key.php

@@ -0,0 +1,120 @@
+<?php
+// API endpoint for revoking API keys (Admin only)
+error_reporting(E_ALL);
+ini_set('display_errors', 0);
+
+// Apply rate limiting
+require_once dirname(__DIR__) . '/middleware/RateLimitMiddleware.php';
+RateLimitMiddleware::apply('api');
+
+ob_start();
+
+try {
+    // Load config
+    require_once dirname(__DIR__) . '/config/config.php';
+
+    // Load models
+    require_once dirname(__DIR__) . '/models/ApiKeyModel.php';
+    require_once dirname(__DIR__) . '/models/AuditLogModel.php';
+
+    // Check authentication via session
+    session_start();
+    if (!isset($_SESSION['user']) || !isset($_SESSION['user']['user_id'])) {
+        throw new Exception("Authentication required");
+    }
+
+    // Check admin privileges
+    if (!isset($_SESSION['user']['is_admin']) || !$_SESSION['user']['is_admin']) {
+        throw new Exception("Admin privileges required");
+    }
+
+    // CSRF Protection
+    require_once dirname(__DIR__) . '/middleware/CsrfMiddleware.php';
+    if ($_SERVER['REQUEST_METHOD'] === 'POST') {
+        $csrfToken = $_SERVER['HTTP_X_CSRF_TOKEN'] ?? '';
+        if (!CsrfMiddleware::validateToken($csrfToken)) {
+            http_response_code(403);
+            throw new Exception("Invalid CSRF token");
+        }
+    }
+
+    // Only allow POST
+    if ($_SERVER['REQUEST_METHOD'] !== 'POST') {
+        http_response_code(405);
+        throw new Exception("Method not allowed");
+    }
+
+    // Get request data
+    $input = json_decode(file_get_contents('php://input'), true);
+    if (!$input) {
+        throw new Exception("Invalid request data");
+    }
+
+    $keyId = (int)($input['key_id'] ?? 0);
+
+    if ($keyId <= 0) {
+        throw new Exception("Valid key ID is required");
+    }
+
+    // Create database connection
+    $conn = new mysqli(
+        $GLOBALS['config']['DB_HOST'],
+        $GLOBALS['config']['DB_USER'],
+        $GLOBALS['config']['DB_PASS'],
+        $GLOBALS['config']['DB_NAME']
+    );
+
+    if ($conn->connect_error) {
+        throw new Exception("Database connection failed");
+    }
+
+    // Get key info for audit log
+    $apiKeyModel = new ApiKeyModel($conn);
+    $keyInfo = $apiKeyModel->getKeyById($keyId);
+
+    if (!$keyInfo) {
+        throw new Exception("API key not found");
+    }
+
+    if (!$keyInfo['is_active']) {
+        throw new Exception("API key is already revoked");
+    }
+
+    // Revoke the key
+    $success = $apiKeyModel->revokeKey($keyId);
+
+    if (!$success) {
+        throw new Exception("Failed to revoke API key");
+    }
+
+    // Log the action
+    $auditLog = new AuditLogModel($conn);
+    $auditLog->log(
+        $_SESSION['user']['user_id'],
+        'revoke',
+        'api_key',
+        $keyId,
+        ['key_name' => $keyInfo['key_name'], 'key_prefix' => $keyInfo['key_prefix']]
+    );
+
+    $conn->close();
+
+    // Clear output buffer
+    ob_end_clean();
+
+    // Return success
+    header('Content-Type: application/json');
+    echo json_encode([
+        'success' => true,
+        'message' => 'API key revoked successfully'
+    ]);
+
+} catch (Exception $e) {
+    ob_end_clean();
+    header('Content-Type: application/json');
+    http_response_code(isset($conn) ? 400 : 500);
+    echo json_encode([
+        'success' => false,
+        'error' => $e->getMessage()
+    ]);
+}