Move Radar and Terrain shading into the Overlays panel

Both used to be their own separate sidebar icons; neither has
anything to manage beyond on/off, same as Wikipedia already got its
own Overlays entry for. Terrain shading is a plain checkbox item now.
Radar keeps its scrub/forecast controls, but behind an explicit
expand (clicking its name), separate from the checkbox — checking it
on shouldn't force the details open, and expanding to scrub/check the
forecast shouldn't also flip the layer on.

Both controls now build their own <li> (RadarControl.mount(li),
HillshadeControl.mount(li) — the latter moved into overlays.js
entirely, it has no reason to live in map.js once it's not building
its own sidebar icon) rather than a whole sidebar-item + flyout the
way they used to.

Also gave each Overlays item a leading icon: Wikipedia and Terrain
shading reuse existing NPS pictograms (WIKI_ICON, and WILDERNESS_ICON
newly exported from icons.js's forest entry — NPS has no dedicated
mountain/terrain glyph, wilderness-22.svg is the closest honest
match). Radar's is hand-drawn (a rain cloud) since NPS's set has
nothing weather-related to reuse.

public/js/map.js

@@ -4,7 +4,6 @@ import {
   Popup,
   addProtocol,
 } from "/vendor/maplibre-gl/maplibre-gl.mjs";
-import { RadarControl } from "/js/radar.js";
 import { GpxPanelControl } from "/js/gpx.js";
 import { OverlaysControl } from "/js/overlays.js";
 import { GnssControl } from "/js/gnss.js";
@@ -14,7 +13,7 @@ import { MeasureControl } from "/js/measure.js";
 import { NotesControl } from "/js/notes.js";
 import { PluginsControl } from "/js/plugins.js";
 import { LocateControl } from "/js/locate.js";
-import { LAYERS_ICON, HILLSHADE_ICON } from "/js/icons.js";
+import { LAYERS_ICON } from "/js/icons.js";
 import { formatCoords, formatSunInfo } from "/js/sun.js";
 import { notifySidePanelOpen, onlyOneSidePanelOpen } from "/js/panels.js";
 import { isLoggedIn } from "/js/auth.js";
@@ -310,100 +309,6 @@ class LayerToggleControl {
   }
 }
 
-const HILLSHADE_ID = "hillshade-dem";
-const COLOR_RELIEF_ID = "elevation-tint";
-// Hypsometric tint reusing this app's own palette (wood_a's green at
-// valley floor, the road casing brown through the mid-slopes) rather than
-// a generic rainbow ramp, so it reads as part of the same map rather than
-// a bolted-on overlay. Stops picked for Central European terrain — the
-// Tatras top out around 2600m — not a general-purpose world ramp.
-const ELEVATION_COLOR_RAMP = [
-  "interpolate",
-  ["linear"],
-  ["raster-value"],
-  0, "#c3e8ab",
-  400, "#dcd08f",
-  900, "#c9a66b",
-  1600, "#a89a86",
-  2600, "#f9f6ef",
-];
-// Public, unauthenticated, no API key — the same open (SRTM/ArcticDEM-derived)
-// elevation tiles OpenStreetMap's own hillshade layer and many other free
-// tools use. Only reachable online; while the offline basemap is active this
-// is skipped in favor of a local terrain.pmtiles if one's been generated
-// (see docs/development.adoc), same optional-local-file story as
-// offline.pmtiles itself.
-const ONLINE_TERRAIN_TILES = ["https://s3.amazonaws.com/elevation-tiles-prod/terrarium/{z}/{x}/{y}.png"];
-
-// A simple on/off sidebar toggle, not a panel — there's nothing to choose,
-// just whether the shading shows.
-class HillshadeControl {
-  constructor(map) {
-    this._map = map;
-    this._active = false;
-    this._offlineAvailable = false;
-    // setStyle() (switching Online/Offline) tears down all custom
-    // sources/layers — put hillshade back if it was on.
-    map.on("style.load", () => {
-      if (this._active) this._addLayer();
-    });
-  }
-
-  mount(sidebar) {
-    this._container = document.createElement("div");
-    this._container.className = "sidebar-item";
-    this._container.innerHTML = `<button type="button" class="sidebar-icon" title="Terrain shading" aria-label="Terrain shading" aria-pressed="false">${HILLSHADE_ICON}</button>`;
-    this._button = this._container.querySelector(".sidebar-icon");
-    this._button.addEventListener("click", () => this._toggle());
-    sidebar.appendChild(this._container);
-  }
-
-  setOfflineAvailable(available) {
-    this._offlineAvailable = available;
-  }
-
-  _toggle() {
-    this._active = !this._active;
-    this._button.classList.toggle("active", this._active);
-    this._button.setAttribute("aria-pressed", String(this._active));
-    if (this._active) this._addLayer();
-    else this._removeLayer();
-  }
-
-  _addLayer() {
-    if (this._map.getSource(HILLSHADE_ID)) return;
-
-    const source = this._offlineAvailable
-      ? { type: "raster-dem", url: `pmtiles://${window.location.origin}/tiles/terrain.pmtiles`, encoding: "terrarium" }
-      : {
-          type: "raster-dem",
-          tiles: ONLINE_TERRAIN_TILES,
-          tileSize: 256,
-          encoding: "terrarium",
-          maxzoom: 15,
-          attribution: "Terrain tiles: Mapzen, SRTM, ArcticDEM",
-        };
-    this._map.addSource(HILLSHADE_ID, source);
-    // Elevation tint under, hillshade on top: the tint sets the base color
-    // per elevation band, hillshade multiplies slope-shading over it — the
-    // combined "characteristic relief look" the TODO asked for, not two
-    // independent layers.
-    this._map.addLayer({
-      id: COLOR_RELIEF_ID,
-      type: "color-relief",
-      source: HILLSHADE_ID,
-      paint: { "color-relief-color": ELEVATION_COLOR_RAMP, "color-relief-opacity": 0.7 },
-    });
-    this._map.addLayer({ id: HILLSHADE_ID, type: "hillshade", source: HILLSHADE_ID, paint: { "hillshade-exaggeration": 0.4 } });
-  }
-
-  _removeLayer() {
-    if (this._map.getLayer(HILLSHADE_ID)) this._map.removeLayer(HILLSHADE_ID);
-    if (this._map.getLayer(COLOR_RELIEF_ID)) this._map.removeLayer(COLOR_RELIEF_ID);
-    if (this._map.getSource(HILLSHADE_ID)) this._map.removeSource(HILLSHADE_ID);
-  }
-}
-
 // A small map-corner button (grouped with Home/zoom, see below) that's a
 // second entry point to the same panel LayerToggleControl already manages
 // in the page's own sidebar — matching the National Park Service's own
@@ -591,8 +496,6 @@ sidebar.insertAdjacentHTML("beforeend", `<div class="sidebar-group-label" title=
 new GpxPanelControl(map, profilePanel).mount(sidebar);
 const overlaysControl = new OverlaysControl(map);
 overlaysControl.mount(sidebar);
-const hillshadeControl = new HillshadeControl(map);
-hillshadeControl.mount(sidebar);
 // Running a plugin needs a login (POST /api/plugins/:name/run) — same
 // "hide the write-only affordance" story as NotesControl above.
 if (isLoggedIn()) new PluginsControl(map).mount(sidebar);
@@ -600,7 +503,6 @@ if (isLoggedIn()) new PluginsControl(map).mount(sidebar);
 sidebar.insertAdjacentHTML("beforeend", `<div class="sidebar-group-label" title="Offline hub"></div>`);
 layerToggle.mount(sidebar);
 layerToggle.setActive("online");
-new RadarControl(map).mount(sidebar);
 
 sidebar.insertAdjacentHTML("beforeend", `<div class="sidebar-group-label" title="Navigation"></div>`);
 gnssControl.mount(sidebar);
@@ -645,7 +547,7 @@ fetch("/api/offline-tiles")
 
 fetch("/api/terrain-tiles")
   .then((response) => response.json())
-  .then(({ available }) => hillshadeControl.setOfflineAvailable(available))
+  .then(({ available }) => overlaysControl.setHillshadeOfflineAvailable(available))
   .catch(() => {});
 
 fetch("/api/kiwix")