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
Create notes_test.go with tests:
- TestNotes_List: list all notes on a task
- TestNotes_Create: create new note
- TestNotes_Update: update note comment
- TestNotes_Delete: delete note
Add testdata/notes/ fixtures:
- list.json: sample notes list
All 4 tests pass using httptest.Server mocking.
Closes checkvist-api-bbx
