(feat) Add unmanaged sample container support

[aurthurm]

Summary

senate.storage currently assumes every StorageSamplesContainer is grid-managed, with samples assigned to fixed row/column positions. That model works for boxes, racks, and trays, but it does not support some storage cases where samples are stored in containers without slot-level position tracking.

This gap blocks use cases such as:

• bags or bins of samples
• temporary holding containers
• bulk archival containers
• other physical containers where only container membership matters

Problem

At the moment:

• StorageSamplesContainer requires managed positions
• store/recover flows assume a position is always needed
• container sample listings assume a position column always exists
• sample viewlets display a position unconditionally

Expected behavior

We need StorageSamplesContainer to support two modes:

• managed: existing row/column position tracking
• unmanaged: samples are stored in the container without fixed positions

For unmanaged containers:

• storing a sample must not require a position
• row/column grid assumptions must not drive validation
• sample listings and sample viewlets must not display meaningless positions
• an optional physical_capacity can be used to enforce a hard sample count limit
• edit forms should show only the relevant fields for the selected mode