Implement API Key Management System

## Overview
Build a complete API key management system with CRUD operations, rotation, expiration, and usage tracking.

## Business Value
API keys enable programmatic access to the platform. This is essential for integrations and automation.

## Technology Stack
- Backend: Go, JWT/Token generation, Middleware
- Frontend: TypeScript, React, Next.js
- Database: PostgreSQL
- Security: Secure key generation and storage

## Skill Level Required
- Intermediate
- Understanding of authentication and authorization
- Knowledge of secure token generation
- Experience with middleware patterns
- Security best practices awareness

## Learning Opportunities
- Learn API key generation and management best practices
- Understand secure token storage and hashing
- Practice building authentication middleware
- Gain experience with key rotation strategies
- Learn about usage tracking and analytics

## Impact
This feature enables programmatic access to the platform, opening up integration possibilities. Contributors will work on security-critical code and learn authentication patterns used across the industry.

## Current State
- Database table exists (api_keys)
- No API endpoints for key management
- No UI for key management

## Subtasks
- [ ] Create API key generation service
- [ ] Implement API key CRUD endpoints
- [ ] Add API key authentication middleware
- [ ] Create API key management UI
- [ ] Implement key rotation
- [ ] Add expiration handling
- [ ] Track key usage statistics
- [ ] Add key revocation

## Implementation Steps
1. Create backend/internal/auth/api_key.go service
2. Add API endpoints: GET, POST, PUT, DELETE /api/v1/api-keys
3. Update authentication middleware to support API keys
4. Create frontend API key management component
5. Add usage tracking

## Getting Started
1. Review existing authentication code in backend/internal/auth/
2. Study secure key generation practices
3. Check middleware implementation in backend/internal/middleware/
4. Review frontend authentication components

## Acceptance Criteria
- [ ] Users can create API keys
- [ ] Keys can be rotated
- [ ] Keys can expire
- [ ] Key usage is tracked
- [ ] Keys can be revoked
- [ ] UI shows key list and details
- [ ] API authentication works with keys

## Estimated Effort
- Hours: 16-20
- Complexity: Medium