Add bb init readiness checks

[codeforester]

Summary

• Add bb init to initialize migrations and v2 financial storage roots for the active data home.
• Extend bb status with v2 storage readiness and managed financial path output.
• Document the v2 initialization path in README, changelog, and AI context.

Validation

• uv run pytest tests/test_bb_cli.py tests/test_bb_storage.py tests/test_packaging.py -q
• ./tests/validate.sh
• git diff --check
• git diff --cached --check

Closes #130