feat: implement persistent storage with SQLite

[anxkhn]

Problem Description

The application uses in-memory storage which loses all data on restart.

Context

A persistent storage solution is needed for production use while maintaining the in-memory option for development.

Files to Investigate

• src/lib/store.ts - Current store implementation
• Create new src/lib/db.ts - Database connection

Expected Behavior

Events should persist across server restarts with SQLite database.

Acceptance Criteria

• SQLite database integration
• Migration system for schema changes
• Environment variable to switch between in-memory and persistent storage
• All existing tests still pass

Suggested Approach

Use better-sqlite3 or libsql for SQLite integration with a repository pattern.

Difficulty: Hard

Estimated time: 3-6 hours
Prerequisites: SQL, database design
Learning outcomes: Database integration, repository pattern