[Week7 - pky] Task1: Add DELETE endpoints and input validation

[kunyoungp]

Summary

• Added DELETE /notes/{note_id} endpoint (204 No Content, 404 if missing)
• Added GET /action-items/{item_id} and DELETE /action-items/{item_id} endpoints
• Added Pydantic Field constraints for input validation:
  • NoteCreate: title (1-200 chars), content (1-10,000 chars)
  • ActionItemCreate: description (1-2,000 chars)
  • NotePatch / ActionItemPatch: same constraints on optional fields

Test plan

• test_delete_note — delete returns 204, subsequent GET returns 404
• test_delete_note_not_found — delete non-existent note returns 404
• test_note_validation_empty_title — empty title returns 422
• test_note_validation_title_too_long — title >200 chars returns 422
• test_get_action_item_by_id — GET returns 200 with correct data
• test_get_action_item_not_found — GET non-existent returns 404
• test_delete_action_item — delete returns 204
• test_delete_action_item_not_found — delete non-existent returns 404
• test_action_item_validation_empty_description — empty description returns 422
• All 12 tests pass (make test)

Notable tradeoffs

• DELETE returns 204 with no body (REST convention) rather than returning the deleted object
• Field constraints use Pydantic v2 Field() for declarative validation rather than custom validators
• NotePatch optional fields use Field(None, min_length=1, ...) so validation only triggers when a value is provided

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