feat: Neuroglancer Views page (PR 4/6, ngviews-04-views-page)

[allison-truhlar]

Neuroglancer Views — PR 4 of 6 (ngviews-04-views-page)

Stacked on #424 (ngviews-03-multiselect). Read-only scope. Adds the /ngviews page and the state layer PR 5/6 build on.

What's in it

• viewQueries.ts — types mirroring backend model.py (View/ViewLayer/ViewCreateRequest/…) + CRUD hooks for /api/neuroglancer/views (list unwraps {views:[...]}, 404→[]). Mirrors ngLinkQueries.
• ViewsContext — provider bundling the CRUD hooks (mirrors NGLinkContext).
• Layer Cart — neuroglancerCart stored in the existing user-preference blob (no new table/endpoint), exposed via a thin CartContext (add/remove/clear, dedup on fsp+path+channel) and a standalone useCartCount hook for the nav badge.
• useNGViewsColumns — Saved Views table columns (name / layers / sharing / updated / actions). Row actions are flat menu items (Open in Neuroglancer, Copy NG link, Download JSON state via the existing downloadTextFile util, Rename, Delete).
• /ngviews page — local-state tabs: Saved Views (TableCard) + a minimal Layer Cart shell (list + remove + clear). Rename/Delete dialogs. No page-level "New View" button — Views are created by cart checkout (PR 5) / scratch save (PR 6).
• Nav + routing — "NG Links" → "NG Views" with a passive cart-count badge; /nglinks → /ngviews redirect (legacy /ng/{key} short-link serving routes untouched).
• Removed the obsolete "Neuroglancer Links" guided-tour workflow (the redirect orphaned it; the page it toured is gone).

Deferred / carry items

• sharing_mode is a stored label only (displayed, not enforced) — per PR 2 decisions.
• "Open" opens the external Neuroglancer URL as a stand-in; PR 6 repoints it to the embedded /ngview/:read_key viewer.
• Layer Cart tree + "Create View" checkout are PR 5; embedded viewer is PR 6.
• Not automated: manual smoke of the redirect + a live cart-badge bump (needs PR 5's cart-mutation UI).

Testing

• Full frontend suite green: 316/316 (pixi run test-frontend). New unit/component tests for viewQueries, CartContext, ngViewsColumns, NGViews; NavbarBadge test updated. node-check / node-prettier-check / node-eslint-check clean (one pre-existing unrelated lint warning).

Built via subagent-driven development from docs/superpowers/plans/2026-08-07-ngviews-04-views-page.md.