Orbit: preserve/validate unique sample labels before launching DESeq2 (generic labels cause failures)

In a DEG run, count tables carried generic/duplicate labels (e.g. `0`, `1`, `2`, or identical `Counts Table` names), producing non-unique identifiers that prevented DESeq2 from running. Orbit eventually worked around it by downloading and re-uploading the count tables with unique names, but that's a manual detour.

Orbit should preserve original sample identifiers from the upstream collection and validate that labels are unique (and non-generic) before launching DESeq2, rather than failing and recovering by re-upload.

Related to #208 (collection handling) and to the fold-change interpretation issue #289.

Start by tracing Orbit's count-table collection handling into the DESeq2 launch path, using the relationship to #208 as context. Confirm where upstream sample identifiers are lost and where labels can be checked; done means original identifiers are preserved and duplicate or generic labels are rejected before DESeq2 starts.

Written by the indexing model from the issue text.