feat(integrations): add omp support

[omar2535]

Description

Add Oh My Pi support.

This adds the omp integration, scaffolding Spec Kit slash commands into
.omp/commands/ and using AGENTS.md for agent context.

Testing

• Tested locally with .venv/bin/specify --help
• Ran targeted tests with:
  uv sync --extra test && uv pip install -e . && .venv/bin/python -m pytest tests/integrations/test_integration_omp.py tests/integrations/test_registry.py tests/integrations/test_integration_catalog.py tests/test_agent_config_consistency.py -q
• Tested with a sample project:
  specify init <tmp>/omp-test --integration omp --script sh --ignore-agent-tools
• Verified generated files:
  • .omp/commands/speckit.constitution.md
  • AGENTS.md
  • .specify/integrations/omp.manifest.json

AI Disclosure

• I did not use AI assistance for this contribution
• I did use AI assistance (describe below)

Code was generated with GPT and Sonnet, then manually reviewed and verified locally by me.