refactor: extract data layer with repository pattern

[anxkhn]

Problem Description

Data access logic is tightly coupled with business logic in the store.ts file.

Context

Repository pattern separates data access from business logic, making the codebase more maintainable.

Files to Investigate

• src/lib/store.ts - Current implementation
• src/actions/events.ts - Server actions using store

Expected Behavior

Data access should be abstracted behind a repository interface.

Acceptance Criteria

• Create IEventRepository interface
• Implement InMemoryEventRepository
• Update actions to use repository
• All tests pass

Suggested Approach

Define repository interface, extract current store logic into InMemoryEventRepository implementation.

Difficulty: Hard

Estimated time: 3-6 hours
Prerequisites: Design patterns, TypeScript interfaces
Learning outcomes: Repository pattern, clean architecture