TSV input format support

[vmvarela]

Part of #68
Depends on #95 (format plugin architecture)

Description

Add TSV as an input format. TSV output already exists via --tsv; this adds the symmetric input side. Trivial since it's just a different delimiter for the existing CSV reader.

Acceptance Criteria

• --input-format tsv reads tab-separated input correctly
• Column names are read from the first row (same as CSV behavior)
• Rows with embedded tabs (quoted) are handled correctly
• Existing --tsv output flag is unchanged and still works
• --output-format tsv is equivalent to --tsv (alias)

Notes

• Implementation: pass tab as the delimiter to the existing CSV reader — should be a 1-line change after Format plugin architecture for multi-format I/O #95
• TSV is common in bioinformatics (BED, VCF-adjacent formats) and Unix pipelines