Add a Hiking trails overlay (Waymarked Trails, online only)

New Overlays panel toggle, same plain on/off shape as Contour lines —
raster tiles from waymarkedtrails.org, which already color each route
by its OSM colour tag (the KST/KČT paint-blaze colors used in
Slovakia/Czechia, plain red elsewhere), so no styling work needed here.

Online only for now; offline (baked into offline.pmtiles) needs a
custom Planetiler profile for route relations, deferred until there's
a route planner/router to pair it with.

public/js/overlays.js

@@ -5,6 +5,7 @@ import { svgToImageData, badgeImageId, escapeHtml } from "/js/gpx.js";
 import { RadarControl } from "/js/radar.js";
 import { ShadowControl } from "/js/shadow.js";
 import { ContourControl } from "/js/contour.js";
+import { HikingTrailsControl } from "/js/hiking_trails.js";
 
 const ICON_IMAGE_SIZE = 48; // rasterized once at this size, rendered much smaller by icon-size below
 const ICON_SIZE = 0.3; // 48 * 0.3 = ~14px, sized to sit inside the marker badge below
@@ -184,6 +185,7 @@ export class OverlaysControl {
     this._radar = new RadarControl(map);
     this._shadow = new ShadowControl(map);
     this._contour = new ContourControl(map);
+    this._hikingTrails = new HikingTrailsControl(map);
     this._wikiEnabled = false; // the checkbox's own state
     this._wikiMoveHandler = null; // the moveend listener driving its live refetch, while enabled
     this._wikiRequestSeq = 0; // ignores an in-flight refetch a newer one has already superseded
@@ -217,13 +219,15 @@ export class OverlaysControl {
       <li class="overlays-panel__item overlays-panel__item--expandable"></li>
       <li class="overlays-panel__item overlays-panel__item--expandable"></li>
       <li class="overlays-panel__item"></li>
+      <li class="overlays-panel__item"></li>
     `;
-    const [hillshadeItem, wikiItem, radarItem, shadowItem, contourItem] = list.children;
+    const [hillshadeItem, wikiItem, radarItem, shadowItem, contourItem, hikingTrailsItem] = list.children;
     this._hillshade.mount(hillshadeItem);
     this._mountWiki(wikiItem);
     this._radar.mount(radarItem);
     this._shadow.mount(shadowItem);
     this._contour.mount(contourItem);
+    this._hikingTrails.mount(hikingTrailsItem);
 
     onlyOneSidePanelOpen(this._panel, () => this._icon.classList.remove("active"));