Address - issue #1612

• reduces the default SQLite busy_timeout from 30 seconds to 5 seconds and makes it configurable via an environment variable.

Acceptance Criteria

• Default timeout reduced to 5000ms (5 seconds)
• Timeout configurable via DB_SQLITE_BUSY_TIMEOUT environment variable
• .env.example documents the setting
• Setting follows db_* naming convention
• No regression in existing tests
• Passes make verify