feat(tile-proxy): Thunderforest Outdoors as foreign karte upstream

OpenTopoMap's hypsometric tint reads "red mountains / green flats" and
looks nothing like the Swisstopo Pixelkarte the proxy hands out
in-region — produced a jarring visual seam right at the CH/LI border.
Thunderforest Outdoors has a muted topo palette + subtle hillshade
that matches the swisstopo tile aesthetic much more closely, so use
it as the abroad `karte` upstream when an API key is available.

- `tile-proxy/build.rs`: reads `tile-proxy/.env` (gitignored) at build
  time and forwards each `KEY=VAL` line to rustc as `--env`, so the
  key is baked into the binary via `option_env!` and never touched at
  runtime. A shell env var of the same name wins over the .env entry
  (dotenv precedence). `cargo:rerun-if-changed=.env` +
  `cargo:rerun-if-env-changed` force a recompile whenever the value
  changes — no stale key cached in the binary.
- `main.rs`: `THUNDERFOREST_API_KEY` read via `option_env!`; foreign
  `karte` is Thunderforest Outdoors when set, OpenTopoMap fallback
  when absent. Behaviour unchanged for keyless builds.
- `mapTiles.ts`: page-footer attribution credits Thunderforest + OSM
  alongside the existing swisstopo / OpenTopoMap / Esri lines so the
  attribution stays correct regardless of which build is deployed.
- `.gitignore`: tile-proxy build artefacts (binary, `target/`, `.env`)
  moved to the root gitignore with fully-qualified paths so the
  source tree isn't hidden by a nested gitignore quirk; the per-dir
  `tile-proxy/.gitignore` is removed.
- README + systemd service: documentation refreshed for the new
  build-time key flow.

package.json

@@ -1,6 +1,6 @@
 {
 	"name": "homepage",
-	"version": "1.93.0",
+	"version": "1.94.0",
 	"private": true,
 	"type": "module",
 	"scripts": {