orientation and channel preview

## Summary

Add an optional QC step to SPIMpack that helps users visually validate image orientation and channel labels before finalizing dataset packaging.

The idea is to load a low-resolution version of each dataset for a set of candidate orientation strings, generate browser-viewable previews, and let the user confirm which orientation produces anatomically correct labels/views. This same workflow could also support visual confirmation or editing of channel labels.

## Motivation

SPIM datasets may require manual verification of:
- orientation strings
- anatomical direction labels
- channel naming / assignment

A lightweight visual QC step would reduce metadata mistakes before packaging into BIDS.

Since `ZarrNii.from_file(..., level=5, orientation=...)` can load low-resolution data and `img.to_nifti()` can easily export to NIfTI, this seems feasible without needing full-resolution data in memory.

## Proposed approach

Implement an **optional QC/orientation preview command** in SPIMpack.

High-level flow:
1. For a dataset, read a low-resolution image with one or more candidate orientation strings, e.g.:
- `ZarrNii.from_file("....ims", level=5, orientation="RPI")`
2. Export the low-resolution oriented image to NIfTI via `img.to_nifti()`
3. Open a lightweight web-based viewer for interactive orthoview inspection
4. Let the user:
- compare candidate orientations
- confirm which orientation is correct
- visually inspect channels
- confirm or edit channel labels
5. Save the accepted orientation/channel metadata for downstream packaging

## Viewer idea

A lightweight browser-based viewer such as **Niivue** seems like a good fit here, since:
- the QC data can be exported to NIfTI
- orthoview inspection is the main use case
- it avoids requiring a heavy desktop GUI

A minimal implementation could also begin with a simple local web app that loads generated low-res NIfTI files and allows selection between candidate orientations and channels.

## Suggested scope for v1

- Add a CLI subcommand such as:
-`spimpack qc preview `
- Support a user-provided or default list of candidate orientations
- Generate low-resolution oriented previews only
- Convert previews to NIfTI
- Launch a small local web UI for review
- Record the user’s selected orientation and confirmed/edited channel labels

## Nice-to-have follow-ups

- Side-by-side comparison of two candidate orientations
- Saved screenshots / provenance artifacts
- Heuristics to rank likely orientations
- Batch QC across multiple datasets
- Snapshot-only/headless mode for CI or remote review

## Open questions

- What should the CLI/API look like?
- Should v1 support a fixed shortlist of candidate orientations or arbitrary user input?
- Where should accepted QC decisions be stored?
- Should channel review be in scope for the initial implementation, or should orientation QC land first?

## Acceptance criteria

- User can run an optional QC command on a dataset
- SPIMpack loads a low-resolution preview for one or more candidate orientations
- Preview data can be inspected in a lightweight browser-based viewer
- User can select/confirm the correct orientation
- User can inspect and confirm/edit channel labels
- The selected metadata is persisted for later packaging steps