chore: remove legacy onboarding dead code
Delete disabled onboarding/observation/firstday_checkin talent files,
tests, CLI commands, and all stale references. Set first_daily_ready
unconditionally on first daily analysis (was gated on onboarding
completion status that no longer exists). Rename test_onboarding.py
to test_convey_apps.py retaining only the live convey app tests.
9 files deleted, ~3700 lines removed across 35 files.