Add comprehensive database integration, authentication, and admin dashboard

This commit introduces major enhancements to Talk2Me:

## Database Integration
- PostgreSQL support with SQLAlchemy ORM
- Redis integration for caching and real-time analytics
- Automated database initialization scripts
- Migration support infrastructure

## User Authentication System
- JWT-based API authentication
- Session-based web authentication
- API key authentication for programmatic access
- User roles and permissions (admin/user)
- Login history and session tracking
- Rate limiting per user with customizable limits

## Admin Dashboard
- Real-time analytics and monitoring
- User management interface (create, edit, delete users)
- System health monitoring
- Request/error tracking
- Language pair usage statistics
- Performance metrics visualization

## Key Features
- Dual authentication support (token + user accounts)
- Graceful fallback for missing services
- Non-blocking analytics middleware
- Comprehensive error handling
- Session management with security features

## Bug Fixes
- Fixed rate limiting bypass for admin routes
- Added missing email validation method
- Improved error handling for missing database tables
- Fixed session-based authentication for API endpoints

🤖 Generated with [Claude Code](https://claude.ai/code)

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

admin/static/css/admin.css

@@ -0,0 +1,192 @@
+/* Admin Dashboard Styles */
+
+body {
+    background-color: #f8f9fa;
+    padding-top: 56px; /* For fixed navbar */
+}
+
+/* Cards */
+.card {
+    border: none;
+    box-shadow: 0 0.125rem 0.25rem rgba(0, 0, 0, 0.075);
+    transition: transform 0.2s;
+}
+
+.card:hover {
+    transform: translateY(-2px);
+    box-shadow: 0 0.5rem 1rem rgba(0, 0, 0, 0.15);
+}
+
+.card-header {
+    background-color: #fff;
+    border-bottom: 1px solid #e3e6f0;
+    font-weight: 600;
+}
+
+/* Status Badges */
+.badge {
+    padding: 0.375rem 0.75rem;
+    font-weight: normal;
+}
+
+.badge.bg-success {
+    background-color: #1cc88a !important;
+}
+
+.badge.bg-warning {
+    background-color: #f6c23e !important;
+    color: #000;
+}
+
+.badge.bg-danger {
+    background-color: #e74a3b !important;
+}
+
+/* Charts */
+canvas {
+    max-width: 100%;
+}
+
+/* Tables */
+.table {
+    font-size: 0.875rem;
+}
+
+.table th {
+    font-weight: 600;
+    text-transform: uppercase;
+    font-size: 0.75rem;
+    color: #6c757d;
+}
+
+/* Login Page */
+.login-container {
+    min-height: 100vh;
+    display: flex;
+    align-items: center;
+    justify-content: center;
+}
+
+/* Responsive adjustments */
+@media (max-width: 768px) {
+    .card-body h2 {
+        font-size: 1.5rem;
+    }
+    
+    .btn-group {
+        display: flex;
+        flex-direction: column;
+    }
+    
+    .btn-group .btn {
+        border-radius: 0.25rem !important;
+        margin: 2px 0;
+    }
+}
+
+/* Loading spinners */
+.spinner-border-sm {
+    width: 1rem;
+    height: 1rem;
+}
+
+/* Error list */
+.error-item {
+    padding: 0.5rem;
+    border-bottom: 1px solid #dee2e6;
+}
+
+.error-item:last-child {
+    border-bottom: none;
+}
+
+.error-type {
+    font-weight: 600;
+    color: #e74a3b;
+}
+
+.error-time {
+    font-size: 0.75rem;
+    color: #6c757d;
+}
+
+/* Toast notifications */
+.toast {
+    background-color: white;
+    box-shadow: 0 0.5rem 1rem rgba(0, 0, 0, 0.15);
+}
+
+/* Animations */
+@keyframes pulse {
+    0% {
+        opacity: 1;
+    }
+    50% {
+        opacity: 0.5;
+    }
+    100% {
+        opacity: 1;
+    }
+}
+
+.updating {
+    animation: pulse 1s infinite;
+}
+
+/* Dark mode support */
+@media (prefers-color-scheme: dark) {
+    body {
+        background-color: #1a1a1a;
+        color: #e0e0e0;
+    }
+    
+    .card {
+        background-color: #2a2a2a;
+        color: #e0e0e0;
+    }
+    
+    .card-header {
+        background-color: #2a2a2a;
+        border-bottom-color: #3a3a3a;
+    }
+    
+    .table {
+        color: #e0e0e0;
+    }
+    
+    .table-striped tbody tr:nth-of-type(odd) {
+        background-color: rgba(255, 255, 255, 0.05);
+    }
+    
+    .form-control {
+        background-color: #3a3a3a;
+        border-color: #4a4a4a;
+        color: #e0e0e0;
+    }
+}
+
+/* Performance optimization */
+.chart-container {
+    position: relative;
+    height: 40vh;
+    width: 100%;
+}
+
+/* Scrollbar styling */
+::-webkit-scrollbar {
+    width: 8px;
+    height: 8px;
+}
+
+::-webkit-scrollbar-track {
+    background: #f1f1f1;
+}
+
+::-webkit-scrollbar-thumb {
+    background: #888;
+    border-radius: 4px;
+}
+
+::-webkit-scrollbar-thumb:hover {
+    background: #555;
+}