feat(cli): sensorwatch export — flat Parquet deep-analysis surface (LEO-349) (#43)

Adds the sanctioned deep-analysis surface: sensorwatch export streams a --since/--until/--last window through the bounded lenient replay parser into a flat one-row-per-reading-per-sample Parquet file (Snappy), queried consumer-side (DuckDB/Polars/pandas). Six fixed columns in file order: timestamp (µs, UTC), sensor, reading, type, value (nullable), unit. Workspace MSRV 1.82 -> 1.85 (parquet 59.x); same-file powers a fail-closed --out alias guard (path + file identity, hard links included) so an export can never overwrite the history it reads. Skill Recipe 5 carries the protocol guardrails.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>