Remove Beads tracking

[atacan]

Summary

• remove tracked Beads project files and Beads-only agent instructions
• remove Beads merge attributes and Beads-specific ignore rules
• remove CLAUDE.md include for deleted AGENTS.md

Validation

• .venv/bin/python -m pip install -e ".[dev]"
• .venv/bin/python -c "import speechall; print(speechall.name)"
• .venv/bin/python -m build