Add skills and sub-agent architecture

[KKranthi6881]

Summary

• add sub-agent role templates installed by dbt-specify init
• add enterprise skills for traceability, governance, project conventions, and CI evidence
• document composition with dbt-labs/dbt-agent-skills without vendoring their repo
• bump package version to 1.1.0 and include agents in package assets

Verification

• uv run --extra dev ruff check src tests
• uv run --extra dev mypy src
• uv run --extra dev pytest
• uv run python -m build
• uv run python -m twine check dist/*
• verified wheel and sdist contain agents and enterprise skills