feat(collector): add ability to import historical SMART CSV files

[Starosdev]

Summary

Allow users to import historical SMART data from CSV files generated by smartd (stored at `/var/lib/smartmontools/attrlog.MODEL-SERIAL.ata.csv`).

Why

Users switching to Scrutiny lose years of historical SMART data accumulated via smartd. smartd exports attribute logs in a well-defined CSV format that can be parsed and backfilled into InfluxDB.

Acceptance Criteria

• Define import file format (smartd attrlog CSV schema)
• Build parser that maps CSV columns to Scrutiny SMART attribute model
• Add import endpoint or CLI subcommand
• Handle deduplication for overlapping timestamps
• Document the import process