v0.3.1

Added

• --db option and MI_FITNESS_DB_PATH environment variable to override the SQLite database location for sync, export, serve, and doctor; precedence is CLI option > environment variable > default platform location. This enables test and multi-database isolation, which the platformdirs default cannot provide (it ignores LOCALAPPDATA on Windows).
• "How to get user_id and passToken" guidance in the README configuration sections (browser-cookie method and QR-login tooling), referenced from doctor output when no configuration file is found.
• Git Bash virtualenv activation command in the installation instructions.
• Export-sensitivity note in docs/export-format.md and the README privacy sections: exports contain no passToken but do carry plaintext user_id identifier columns and must be handled as sensitive personal data.
• Warn after successful CLI exports when selected datasets contain zero rows; exported JSON/CSV bytes are unchanged (#7, thanks @pollychen-lab).

Changed

• load_config() no longer writes a default config.json on first run; configuration is persisted only by the explicit setup command.
• README test-suite counts updated to the current 46 tests.