Add SQLite database support as an alternative to Redis

[Copilot]

Implements SQLite as an alternative database backend for busuanzi, providing users with a lightweight, serverless option alongside the existing Redis support.

Changes Made

Database Abstraction Layer

• Created process/dbutil package with a unified database interface
• Implemented Redis and SQLite adapters that conform to the same interface
• All database operations now go through this abstraction layer

SQLite Implementation

• Added process/sqliteutil package for SQLite connectivity
• Created proper table schema to handle UV/PV tracking:
  • site_pv: Site page view counters
  • page_pv: Page-specific view counters
  • site_uv: Site unique visitors (replaces Redis HyperLogLog)
  • page_uv: Page unique visitors (replaces Redis HyperLogLog)

Configuration Support

• Extended config.yaml with new database selection options
• Added Database.Type setting to choose between redis and sqlite
• Added SQLite.Path configuration for database file location

Core Changes

• Updated main.go to use the new database abstraction
• Modified core/count.go to work with the unified interface
• Maintained backward compatibility - existing Redis configurations work unchanged

Usage Examples

Redis Configuration (existing):

Database:
  Type: redis
  Prefix: bsz
Redis:
  Address: redis:6379
  Password: ""
  Database: 0

SQLite Configuration (new):

Database:
  Type: sqlite
  Prefix: bsz
SQLite:
  Path: ./busuanzi.db

Benefits

• Simplified deployment: No need for a separate Redis server
• Lower resource usage: SQLite is more lightweight for smaller sites
• Data persistence: SQLite data persists in a single file
• Easy backup: Simple file-based backup and restore
• Development friendly: No external dependencies for local testing

Testing

Verified functionality with comprehensive tests:

• ✅ Database initialization and table creation
• ✅ Page view incrementing and unique visitor tracking
• ✅ Site-wide and page-specific counters
• ✅ API endpoint compatibility
• ✅ Backward compatibility with Redis configurations

This implementation provides users flexibility to choose the database backend that best fits their deployment requirements while maintaining the same API and functionality.

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