feat: add Todoist REST API v2 fake service

[rotemtam]

Summary

• Adds a stateful fake implementation of the Todoist REST API v2 (FastAPI server)
• 10 contract test modules covering the core API surface
• Tests validated against the real Todoist API using grounding mode
• Supersedes feat: add Todoist REST API v1 fake service #31

API Coverage

• Tasks: CRUD, completion/reopening, subtask cascading, recurring due dates
• Projects: CRUD, archiving, nesting, view styles
• Sections: CRUD, ordering, task organization, cascade delete
• Labels: Personal CRUD, shared labels, task association
• Comments: Task/project comments, markdown
• Due Dates & Priorities: Priority mapping, date/datetime, recurring patterns
• Filtering & Search: Priority, label, date, project, AND/OR operators
• Cross-Resource Workflows: Multi-step agent scenarios across resource types

Contract Tests

10 test modules in services/todoist/contracts/:

Module	Coverage
test_task_crud_lifecycle	Task create, read, update, delete
test_task_completion_lifecycle	Close, reopen, recurring reschedule
test_project_management	Project CRUD, archiving, nesting
test_section_organization	Section CRUD, ordering, cascade
test_label_management	Label CRUD, task association
test_comment_threading	Task/project comments
test_subtask_hierarchy	Parent-child relationships, cascading
test_due_dates_and_priorities	Priority values, date formats, recurring
test_task_filtering_and_search	Filter expressions, query operators
test_cross_resource_agent_workflows	End-to-end multi-resource scenarios

Running tests

# Against fake server
DOUBLEAGENT_TODOIST_URL=http://localhost:8080 uv run pytest -v

# Against real Todoist API (grounding mode)
TODOIST_GROUNDING_TOKEN=<real-token> uv run pytest -v

Test plan

• All contract tests pass against fake server
• Contract tests pass against real Todoist API (grounding mode)
• doubleagent run todoist starts the server correctly

🤖 Generated with da-agent + Claude Code

[zozo123]

LGTM