Make the codebase poi-free (poi* → structure*)

docs/BACKLOG.md

@@ -60,13 +60,6 @@ From [ADR 0001 §"explicitly not deciding"](adrs/0001-fade-ownership.md):
 
 Diagnosed but unplanned. Captured here so they don't get lost; promote to a spec or plan when prioritised. Most have richer notes in agent memory (`~/.claude/projects/-Users-rulkens-Development-js-skymap/memory/`).
 
-- **Make the codebase `poi`-free (`poi*` → `structure*`)** — **Priority: high.** The data layer is already `StructureRecord` and the InfoCard family was renamed to `StructureDetailCard` / `CompactStructureCard` (`structure` props, `Structure` eyebrow). The legacy `poi` vocabulary survives in the engine/identity/URL layers and reads as a second name for the same concept — the exact "two names, one thing" wart the simplicity convention flags. Holdouts found 2026-06-07:
-  - **`isPoi` predicate** (`services/engine/isPoi.ts`) — imported by ~8 non-InfoCard sites (`FocusableTarget.d.ts`, `EngineCallbacks.d.ts`, `EngineCameraHandle.d.ts`, `useUrlSync.ts`, `useStructureMemberCount.ts`, `engine.ts`, `commitFocus.ts` + tests). Rename to `isStructure`.
-  - **`POI_CATEGORY_INFO` / `data/poiCategoryInfo.ts` / `PoiCategory` type** (`@types/engine/data/PoiCategory.d.ts`) — the category-info table + its type alias; co-design with the `STRUCTURE_CATEGORY_META` consolidation in the DRY item below (don't merge the genuinely-different category *lists*).
-  - **`poiUrl` / `resolvePoiFromPick`** (`services/url/poiUrl.ts`, `services/engine/helpers/resolvePoiFromPick.ts`) and the engine `selectedPoi` params in `selectionRingPass.ts` / `EngineSubsystemHandles.d.ts` / `engine.ts`.
-  - **⚠️ The `#poi=` deep-link URL param** (`services/url/poiUrl.ts`, `utils/url/hasDeepLink.ts`, `App.tsx`) is a **persisted format** — existing shared links use `#poi=cluster-…`. Renaming the param string would break them, so this needs a back-compat read (accept both `#poi=` and a new `#structure=`) or must be deliberately left as-is. Decide explicitly; do **not** blind-rename.
-
-  **Approach:** run `entanglement-radar` first to map the knots and the `#poi=` back-compat boundary, then apply via `/simplify` (delegate the edits per `feedback_simplify_edits_in_subagent`). Pairs with the `cluster* → structure*` naming migration and the structure-category-identity DRY item below — all three are the same "converge on `Structure*` vocabulary" cleanup. Mechanical apart from the URL-param decision; typecheck + tests are the safety net.
 - **Mobile layout reflow** — hover-on-touch is handled (`disable hover on touch input`, #226: hover-only affordances now route through tap). What remains is the general responsive layout pass: reflow the InfoCard / SettingsPanel / StatusBar for narrow viewports so the UI is usable on a phone, not just non-broken. **Update 2026-06-07:** the InfoCard half is specced — [2026-06-07 mobile bottom-sheet design](superpowers/specs/2026-06-07-mobile-info-card-bottom-sheet-design.md) (awaiting plan); the SettingsPanel launcher is a gated fast-follow pending an `entanglement-radar` pass over `SettingsPanel`.
 - **Lower-tier "close to home" weighting** — retune the small/medium tier subsampling so more galaxies survive near the camera's home position for maximum visual density on first load, while keeping the on-screen count fast. Distinct from the deliberate SDSS far-shell sample (memory `project_sdss_medium_intentionally_far`).
 - **Densely seed the Local Volume across all tiers (group explorability)** — surfaced 2026-06-04 with the `group` category. The 16 Local Volume groups are only interesting to fly into if their *member* galaxies are present, but `subsampleByAbsMag` (`tools/catalog/`) thins the nearby volume by absolute-magnitude cut, so faint dwarfs in the Local Group / M81 / Cen A / Sculptor etc. get culled — a group ring you focus into can be nearly empty at small/medium tier. Bias the subsampling to **keep galaxies inside (or near) the featured group spheres** regardless of `M_abs`, across small + medium and ideally large tiers, so each group has as many members as possible. Related to but distinct from the "close to home" weighting above: that's camera-home density; this is per-group membership density keyed off the structure seed. Implementation hooks: the group seed positions/radii (`data/structure_anchors.seed.json`) are available to the build, so the subsampler can spare points within `apparentRadiusMpc` of each group centre. Keep an eye on the on-screen count budget. Pairs with the cluster-focus member count (`PoiDetailCard` "Galaxies" row) — denser seeding makes that number meaningful at lower tiers.