Add useCardModal composable tests (61 tests)

Cover all branch paths in useCardModal.ts to bring
src/composables branch coverage above the 80% threshold.
Tests exercise: card/isOpen watchers, formattedDueDate,
isOverdue, isFormValid, loadCaptureProvenance success/error,
handleSave with field deltas and error, delete flow with
guard and error, comment CRUD including reply drafts and
nullish coalescing, canEditComment, handleStartEditComment
guards, onBeforeUnmount cleanup, and provenance link
generation.

Author: Chris0Jeky