Recurring tasks only ever showed on their single dueDate. Add a
recurrence engine that expands occurrences per-date with independent
per-occurrence completion.
- TaskItem: recurrenceEnd + completedOccurrences (optional, safe decode).
- TaskViewModel: isOccurrence/occurrenceComplete/toggleOccurrence/
occurrenceCopy/nextOccurrence/occurrences(on:); Daily/Weekly/Monthly/
Yearly/Every-Weekday; respects recurrenceEnd; works across years.
- toggle() routes recurring rows to per-occurrence completion.
- Date filters re-inject per-date occurrence copies; recurring excluded
from overdue. Calendar dots + day detail use occurrences(on:).
Also log KC-11 (year display) + KC-12.
Pending: "repeat until" date UI (engine already honors recurrenceEnd).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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