[allison-truhlar]

Stacked on #476.

What changed

• The Neuroglancer button on Zarr and OME-Zarr metadata panels now creates a View by default. It opens the Create View dialog with the dataset name filled in, then opens the new View. With Views selected, the label under the button reads "Neuroglancer View".
• A new preference switches the button back to standalone Neuroglancer, which works as before.
• A View's "Open in Neuroglancer" link-out now has its own Internal/Public base URL preference, separate from standalone Neuroglancer.
• The Preferences section "Neuroglancer links" is renamed "Neuroglancer" and split into three parts: the button target, Views, and Standalone Neuroglancer (base URL and state generation options). The URL options now read "Internal — hosted by your institution (host)" and "Public — host". Both hostnames come from the viewer config.
• Two new preference keys: neuroglancerButtonTarget (default views) and viewsNeuroglancerUrlSource (default configured). Existing keys are unchanged, so saved preferences carry over.

Follow-ups

• N5 panels still open standalone Neuroglancer, because the Layer Cart checkout (probeDataset) can't read N5 yet.

Testing

• pixi run test-frontend: all tests pass, including a new DataToolLinks test for the View override and its label.
• The Prettier and ESLint pre-push hooks pass.

@krokicki
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