[ticket-002] fix: isolate test_password_store from host dotenv

[tom-sapletta-com]

Ticket 002: fix password store test isolation with dotenv

Changes

• Isolate test_scenario_github_login_only and test_scenario_anthropic_no_creds from host .env via patch('dotenv.load_dotenv')
• Register ticket-002 in TICKETS.md with required governance markers
• All 31 unit tests in test_password_store.py pass cleanly (and 2026 overall unit tests pass)
• Governance gate passes with 0 errors (GOV-PASS)