Map tiles: switch to Esri World Light Gray (OSM 403s file://)

tiles="OpenStreetMap" returned HTTP 403 "referer is required by tile usage
policy" in the target browser — OSM graylists refererless requests and a
karte.html opened via file:// sends no Referer. Esri's Canvas/World_Light_Gray
base + reference layers need neither a key nor a Referer and keep the muted
look. New MAP_TILES / MAP_TILES_LABELS / MAP_TILES_ATTR constants; generate_map
adds them as explicit TileLayers.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

docs/changelog.md

@@ -2,6 +2,16 @@
 
 Notable changes to the app. Newest first.
 
+## 2026-09-07 — map tiles → Esri (OSM 403s local files)
+
+The switch to `tiles="OpenStreetMap"` worked on the dev machine but the target
+laptop's browser got **HTTP 403 "referer is required by tile usage policy"** —
+OSM's CDN blocks refererless requests, and a `karte.html` opened as `file://`
+sends no `Referer`. Switched to **Esri "World Light Gray"** (base + labels
+overlay, `server.arcgisonline.com`): no key, no `Referer` check, muted look
+similar to the old positron. Constants `MAP_TILES` / `MAP_TILES_LABELS` /
+`MAP_TILES_ATTR`.
+
 ## 2026-09-07 — install split for non-admin users
 
 The target account has no sudo, so install is two scripts: