Fix shared_tasks.toml check sequence referencing undefined tasks

[Copilot]

Summary

The shared check sequence in shared_tasks.toml referenced mypy, bandit, and test tasks that weren't defined, breaking poe check for agents without their own implementations.

Added default task definitions:

• mypy: Type-checks src/ using agent's config
• bandit: Security-scans src/ and docs/source/
• test: Runs pytest with coverage

Agents can override these defaults in their pyproject.toml for custom paths/options (as agent1 already does).

Testing

• uv run poe check
• Code review and CodeQL security scan passed

Checklist

• Linked issue or task reference
• Added/updated tests where relevant
• Updated docs/README if needed
• No secrets or sensitive data added
• Considered backward compatibility and deployment impact

Additional context

Maintains existing behavior for agent1 (which overrides all three tasks) while making shared_tasks.toml self-consistent for future agents.

---

💬 We'd love your input! Share your thoughts on Copilot coding agent in our 2 minute survey.

[Copilot]

Pull request overview

This PR fixes a critical issue in shared_tasks.toml where the check sequence referenced three tasks (mypy, bandit, test) that weren't defined, causing poe check to fail for agents without their own implementations.

Changes:

• Added default task definitions for mypy, bandit, and test in shared_tasks.toml
• Added explanatory comment noting agents can override these defaults in their pyproject.toml
• Ensures shared_tasks.toml is self-consistent and works standalone

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.