New stateless components ported from org-mode-agenda-cli reference app:
- view-toggle: Grid/Agenda segmented control
- source-toggles: colored pill buttons for event source filtering
- event-detail-dialog: overlay with title, date, time, tags, source
- error-banner: dismissible error bar
- loading-indicator: pulsing dot for async state
Enhanced existing components:
- calendar-event-grid: added :loading?, :header-actions slots
- agenda-day-group/agenda-list: added :day-actions slot per day header
- Event data format extended with :tags and :source fields
CSS: view toggle, loading pulse animation, error banner, source toggles,
detail dialog overlay — all using theme tokens with dark mode support.
Tests: 126 tests, 794 assertions, 0 failures.
Dev demos updated in all 3 targets with full interactive calendar app.
d8e280df2a