Add the Data Library: live regional datasets, tiles and packs

DATA LAYERS keeps its curated core layers; regional and niche sources
live in the Data Library, opened from Browse data library at the foot
of the panel. Each entry is a JSON manifest in src/library/entries/
pointing at a live upstream (query API, provider-hosted file or tile
endpoint), so nothing is bundled and a self-hosted instance hosts no
data. Sources without CORS go through one allowlisted /api/library
route. Kinds: dataset (GeoJSON, CSV, JSON records, ArcGIS, partitioned
GeoParquet), tiles (XYZ, WMS/ArcGIS bbox export, terrarium relief) and
pack. Selections persist and travel in share links as lib=, separate
from the core layer tokens. Library rows get Zoom and Remove icon
chips that work while the layer is off, rendered through RailChips.
Strings are translated in every locale.

changelog.d/1604-data-library.md

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+- Add the Data Library. New regional and niche sources no longer join the
+  Data Layers panel: **Browse data library** at its foot lists live entries
+  (a manifest each in `src/library/entries/`, fetched from the provider, never
+  bundled) with their licence, coverage and what this instance needs to serve
+  them, and **Add** puts one under a Library heading. Datasets (GeoJSON, CSV,
+  ArcGIS), raster tiles and host-layer packs are supported; selections persist
+  and travel in share links as `lib=`, separate from the layer tokens; one
+  generic `/api/library` proxy serves entries without CORS. Seeded with NASA
+  EONET events, EIA and WRI power plants, NWS alerts, NOAA tide stations,
+  Smithsonian volcanoes, NASA Black Marble, OpenSeaMap seamarks, and the
+  opt-in IMF PortWatch and CCTV packs. FEMA USA Structures and the
+  National Bridge Inventory load what is in view once you zoom in, and
+  Addresscloud's EPC ratings stream from Source Cooperative's GeoParquet on
+  S3, coloured A–G with live legend counts. Open tile overlays (geology,
+  biodiversity, population, surface water, national aerial photos and maps)
+  join GDACS alerts and EPA Superfund and TRI facilities. 64 aerial photo
+  layers from the Open Imagery Register (national programmes across Europe,
+  NSW, NAIP and US state, county and city services, WMS and ArcGIS export
+  included) show their resolution, true-ortho flag, years flown and refresh
+  cycle in Browse; aerial photos stay above every other drape, are clipped to
+  their coverage, and the providers' blank fill no longer whitens the globe.
+  Kartverket's open Norwegian maps (topographic, nautical charts, hillshade,
+  terrain relief, sea depths, boundaries and the cadastre) and Mapterhorn's
+  global terrain, drawn in the browser as shaded relief with an elevation
+  legend, are in the library too. Stat tiles head the dialog. A library layer's row has
+  Zoom to layer and Remove icons, and the dialog has Zoom and a confirmed
+  Remove all (asturksever, #1604).