feat(hikes): worldwide maps via a region-switching tile proxy

Add tile-proxy/: a small Rust (axum) service behind nginx that serves one canonical XYZ scheme (/{karte,luftbild,dufour}/{z}/{x}/{y}) and, per tile, picks the provider by geometry — swisstopo when the tile overlaps a swisstopo-covered region (Switzerland or Liechtenstein, each simplified + 2 km buffer; tile-bbox ∩ polygon at every zoom), otherwise OpenTopoMap (schematic) / Esri World Imagery (satellite), with an auto-fallback for border 404s. Includes the region generator (gen-regions.mjs), a Makefile, nginx caching-proxy + systemd examples, and a README. Listen address is env-driven (TILE_PROXY_ADDR). App side: - New mapTiles.ts is the single source for the proxy URLs + combined attribution; HikeMap / HikesOverviewMap / EditMap fetch through maps.bocken.org instead of swisstopo directly, on-map attribution controls removed, preconnect + footer credits updated (swisstopo / OpenStreetMap+OpenTopoMap / Esri). - Region-aware schematic max zoom (isSwissRegion helper): detail map caps at z17 abroad and hides the CH/LI-only Dufour layer; overview caps at z18 when a shown hike is abroad. - Route-builder: add the satellite layer via the same bottom-right layer popover as the other maps.
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+# tile-proxy
+
+A tiny region-switching map-tile service for the hikes maps. It exposes one
+canonical XYZ scheme and, **per tile**, serves **swisstopo inside Switzerland
+& Liechtenstein** and a **global provider elsewhere** — so a hike anywhere in
+the world gets a good schematic + satellite basemap, while CH/LI hikes keep
+swisstopo quality.
+
+```
+browser / build script
+        │   https://maps.bocken.org/{layer}/{z}/{x}/{y}
+        ▼
+   nginx   ── TLS termination + on-disk tile cache (proxy_cache)
+        ▼   http://$TILE_PROXY_ADDR   (default 127.0.0.1:8765)
+  tile-proxy (this crate)  ── z/x/y → point-in-polygon → pick + fetch upstream
+        ▼
+  swisstopo  │  OpenTopoMap  │  Esri World Imagery
+```
+
+The listen address is set entirely by the **`TILE_PROXY_ADDR`** env var
+(`host:port`); pick whatever port you like. nginx, the systemd unit and this
+binary all reference that one value.
+
+Caching/TLS/rate-limiting live in **nginx** (Arch's stock nginx has no njs, and
+we want a real geometry test anyway). This binary only does routing + fetch and
+is stateless.
+
+## Layers & providers
+
+| `{layer}`  | swisstopo region (CH + LI)       | elsewhere             |
+|------------|----------------------------------|-----------------------|
+| `karte`    | `ch.swisstopo.pixelkarte-farbe`  | OpenTopoMap           |
+| `luftbild` | `ch.swisstopo.swissimage`        | Esri World Imagery    |
+| `dufour`   | `ch.swisstopo.hiks-dufour`       | — (CH/LI-only)        |
+
+The swisstopo region is **Switzerland + Liechtenstein** (swisstopo has
+high-quality data for both). A tile is served by swisstopo when it **overlaps**
+that region at all — the tile's lat/lng rectangle is intersected against the
+polygons (`src/regions.in`, simplified + a **2 km outward buffer**), so *any*
+tile touching CH/LI gets swisstopo, at every zoom. (A swisstopo tile partly
+outside its data just renders white at the edges, which beats a foreign
+provider drawing over covered ground.) For `karte`/`luftbild`, a swisstopo tile
+that 404s near the edge falls back to the global provider automatically.
+
+## Build & run
+
+```sh
+cargo build --release
+TILE_PROXY_ADDR=127.0.0.1:8765 ./target/release/tile-proxy
+# smoke test
+curl -s -o /dev/null -w '%{http_code} %{content_type}\n' \
+  http://127.0.0.1:8765/karte/9/266/180        # Bern  → swisstopo (jpeg)
+curl -s -o /dev/null -w '%{http_code} %{content_type}\n' \
+  http://127.0.0.1:8765/karte/9/255/171        # London → OpenTopoMap (png)
+```
+
+`TILE_PROXY_ADDR` defaults to `127.0.0.1:8765` but should be set explicitly.
+`GET /healthz` returns `ok`.
+
+Run it as a service with [`deploy/tile-proxy.service`](deploy/tile-proxy.service)
+and put nginx in front with [`deploy/nginx.conf.example`](deploy/nginx.conf.example).
+
+## Regenerating the region polygons
+
+`src/regions.in` is generated — don't hand-edit it. To refresh (or change the
+buffer / simplification, or add a region):
+
+```sh
+make regions                                    # CH + LI, default 2 km buffer
+BUFFER_KM=2 SIMPLIFY_DEG=0.004 node scripts/gen-regions.mjs
+node scripts/gen-regions.mjs ./ch.geojson ./li.geojson   # local files
+```
+
+It takes each source's largest exterior ring, Douglas–Peucker–simplifies it,
+then pushes every vertex outward by `BUFFER_KM`. Rebuild the binary afterwards
+(the ring is baked in via `include!`). If you move the boundary, purge the nginx
+cache so old tiles aren't served by the previous provider.
+
+## Attribution (required)
+
+All three providers require credit — keep these on the page (the hikes pages
+show them in the footer):
+
+- **© swisstopo** — Swiss tiles.
+- **© OpenStreetMap contributors, SRTM | © OpenTopoMap (CC-BY-SA)** — world schematic.
+- **© Esri, Maxar, Earthstar Geographics** — world satellite.
+
+## Notes
+
+- **Max zoom** differs by provider — clamp the client: OpenTopoMap 17,
+  Esri imagery ~19, swisstopo 19/20.
+- **OpenTopoMap fair-use:** it's a small volunteer project; the long nginx
+  cache + a descriptive `User-Agent` is the mitigation. If traffic grows,
+  self-host a renderer.
+- **Dufour** has no world equivalent — the client hides that layer when the
+  view leaves Switzerland.