Add comprehensive test coverage (target 80%+)

[thedhanawada]

Problem

Current test coverage is ~15-20%. Existing tests cover StateManager, EventForm, and DOMUtils but many modules have zero coverage.

Scope

Add tests for:

• BaseComponent lifecycle
• ForceCalendar (main component) — initialization, view switching, event handling
• MonthViewRenderer
• WeekViewRenderer
• DayViewRenderer
• EventBus — subscription, wildcards, cleanup
• StyleUtils
• DateUtils (interface-specific)

Acceptance Criteria

• 80%+ line coverage
• All renderers have rendering tests (snapshot or DOM assertion)
• Event delegation tested
• View switching tested