Extended `redact_secrets()` coverage to credential-bearing exception handlers in the encrypted-database, web queue, and scheduler subsystems — sites where the user's SQLCipher master password is in lexical scope. Unlike API keys (rotatable), the SQLCipher master password is unrecoverable (TRUST.md §5), so a leak via a rendered traceback or upstream exception message is a permanent compromise. Covers `database/encrypted_db.py` (6 sites in `create_user_database` / `open_user_database` / `change_password`), `web/queue/processor_v2.py:_start_research_directly`, and 11 sites across `scheduler/background.py` (subscription scheduling, document processing, RAG indexing, overdue-subscription handling, subscription research trigger). See #4182.
