feat: add S2 GhostMaps live intel layer

Adds an "S2 GhostMaps" layer (Events group) that renders S2 Underground's
GhostMaps KMZ exports (Common Intelligence Picture, Kinetic 30d, Border
Crisis, Iran CIP/Kinetic, Yemen FLOT, latest incident drop).

- server/providers/ghostMaps.js: watcher polls the repo's git smart-HTTP
  ref advertisement (default every 15s, GHOSTMAPS_POLL_SECONDS), fetches
  the tree only on a new head, caches commit-pinned files by blob sha and
  pushes catalog updates to browsers over SSE (/api/ghostmaps/events).
- src/layers/ghostMaps: KML reader, ArcGIS popup-table parsing, per-product
  data sources, product chips, horizon-culled pins, report cards.
- Unit tests, QA gate (scripts/qa-ghostmaps.mjs), credits (CC BY-NC-SA 4.0),
  i18n, voice manifest, layer-state token 5.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

DATA_SOURCES.md

@@ -38,6 +38,7 @@ How to read this:
 | **Environment and Climate Change Canada** (MSC GeoMet OGC API) | Air quality (AQHI) — Canadian station observations | [ECCC Data Servers End-use Licence](https://eccc-msc.github.io/open-data/licence/readme_en/) (open, attribution required, no endorsement implied) | "Contains information licensed under the Environment and Climate Change Canada Data Servers End-use Licence" |
 | **NASA GIBS** (WMTS tiles + Worldview Snapshots) and **NASA CMR** (granule catalog) | Recent Imagery layer: HLS S30/L30 (Sentinel-2, Landsat 8/9) and VIIRS true-colour tiles draped on the map, per-day thumbnails and PNG exports; the HLS granule catalog (dates, cloud, footprints) for a selected box | U.S. public domain (NASA data); keyless, browser-direct (CORS `*`); no bulk use — one 30-day catalog query per box, tiles bounded to the box, six tile requests in flight | "We acknowledge the use of imagery provided by services from NASA's Global Imagery Browse Services (GIBS), part of NASA's Earth Science Data and Information System (ESDIS)." — [gibs.earthdata.nasa.gov](https://gibs.earthdata.nasa.gov), [HLS](https://lpdaac.usgs.gov/products/hlss30v002/) |
 | **NIFC WFIGS** (Wildland Fire Interagency Geospatial Services, ArcGIS feature service) | Fire Perimeters layer: current interagency wildfire incident perimeters, containment, and incident facts | U.S. public domain (interagency wildland-fire data published through the [NIFC Open Data portal](https://data-nifc.opendata.arcgis.com/)); fetched keyless through `/api/fire-perimeters` (5-minute server cache) with `exceededTransferLimit` paging | "Wildfire perimeters: National Interagency Fire Center (WFIGS)" |
+| **S2 Underground GhostMaps** (`github.com/s2underground/GhostMaps`) | S2 GhostMaps layer: the current edition of S2's KMZ intel products (Common Intelligence Picture, 30-day kinetic pull, Border Crisis Map, Iran and Yemen products, newest incident drop). Keyless. `/api/ghostmaps` reads the branch head from git's ref advertisement every 15 s (`GHOSTMAPS_POLL_SECONDS`, minimum 5 s), lists the tree through the GitHub REST API only when the head changes (optional `GITHUB_TOKEN`), downloads files by commit-pinned raw URLs into `.gev-cache/ghostmaps/` and pushes new catalogs to browsers over server-sent events | [CC BY-NC-SA 4.0](https://creativecommons.org/licenses/by-nc-sa/4.0/) (repository README: "S2 Underground © 2025 by S2A1"); non-commercial, attribution required; files are fetched at runtime, never stored in this repository | "S2 GhostMaps intel products: S2 Underground © by S2A1, CC BY-NC-SA 4.0" — shown in-app |
 | **InciWeb** (inciweb.wildfire.gov)                                    | Per-incident "InciWeb ↗" card links to official incident pages (narratives, evacuation/closure notices) | U.S. government public incident information. Links are matched best-effort by incident name and state, with incident page origin and update times checked on selection. Same-origin `/api/fire-perimeters/inciweb` routes cache the catalog for 1 hour and publication metadata for 30 minutes; linked pages remain InciWeb content | "Incident information: InciWeb (inciweb.wildfire.gov)" |
 | **OpenFreeMap / OpenMapTiles** | Vector tiles | OpenStreetMap data under ODbL 1.0 | OpenFreeMap © OpenMapTiles |
 | **Overture Maps Foundation** | Military area names pack | [ODbL 1.0](https://opendatacommons.org/licenses/odbl/1-0/) | Overture Maps Foundation |