Implement complete Database Administration section in Admin page

Replace 'coming soon' placeholder with fully functional database management tools:

Database Statistics Dashboard:
- Live counts of graphs, nodes, edges, and data integrity issues
- Color-coded metrics with visual indicators
- Real-time updates on demand

Interactive Management Tools:
- Refresh Stats: Update all database counts instantly
- Check Data Integrity: Scan for corrupted records and schema violations
- Cleanup Test Data: Remove duplicate/corrupted graphs (up to 50 per batch)

GraphQL Query Tool:
- Direct database access with syntax-highlighted query editor
- Execute custom queries and mutations
- Built-in sample queries and clear/execute controls
- Real-time result display

Debug Console:
- Timestamped log of all operations and results
- Error tracking and detailed status reporting
- Auto-scroll with historical operation tracking

Features:
- Automatically loads database statistics on component mount
- Identifies and handles corrupted test data (323+ graphs)
- Safe batch operations with user confirmation for destructive actions
- Professional admin interface with consistent styling and responsive layout

Author: mvalancy