Add custom APITime type with UnmarshalJSON to handle the non-standard
date format returned by the Checkvist API ("2026/01/14 16:07:31 +0000")
instead of the expected RFC3339 format.
Changes:
- Add APITime type with custom JSON marshaling/unmarshaling in models.go
- Replace time.Time with APITime for UpdatedAt/CreatedAt fields in
Checklist, Task, and Note structs
- Add NewAPITime constructor for convenience
- Update test fixtures to use real API date format
- Add comprehensive unit tests for APITime in models_test.go
Fixes: checkvist-api-4qn
Add models.go with all data structures:
- Checklist struct with fields for ID, Name, Public, Archived, etc.
- Task struct with full task data including status, priority, due dates
- TaskStatus enum (StatusOpen, StatusClosed, StatusInvalidated)
- Note struct for task comments
- User struct for user information
- Tags type as map[string]bool for efficient lookup
- DueDate struct with smart syntax support and constructors
(DueAt, DueString, DueInDays) and constants (DueToday, DueTomorrow,
DueNextWeek, DueNextMonth)
Closes checkvist-api-e9p
