Switch to vector maps (MapLibre GL JS + PMTiles) and add RainViewer radar

Replace Leaflet/raster tiles with MapLibre GL JS: an online OpenFreeMap
style and an offline style built from a local PMTiles archive via
pmtiles.js and protomaps-themes-base (no glyphs/labels offline by
design, see docs/architecture.adoc). Frontend libraries are vendored
locally rather than loaded from a CDN so the app keeps working with no
internet access.

Also add an animated RainViewer precipitation radar overlay (toggle,
play/pause, scrub slider), matching the default time window of the
weather-radar-card Home Assistant integration.

public/css/style.css

@@ -7,3 +7,72 @@ html, body {
   height: 100%;
   width: 100%;
 }
+
+.layer-toggle {
+  display: flex;
+}
+
+.layer-toggle button {
+  /* Override maplibregl-ctrl-group's 29x29px square icon-button sizing —
+     these are text buttons. */
+  width: auto;
+  height: auto;
+  border: none;
+  background: #fff;
+  padding: 6px 10px;
+  font: inherit;
+  font-size: 13px;
+  white-space: nowrap;
+  cursor: pointer;
+}
+
+.layer-toggle button.active {
+  background: #dbe9ff;
+  font-weight: 600;
+}
+
+.radar-control {
+  display: flex;
+  flex-direction: column;
+  gap: 4px;
+  padding: 6px 8px;
+  font-size: 13px;
+}
+
+.radar-control__toggle {
+  display: flex;
+  align-items: center;
+  gap: 6px;
+  cursor: pointer;
+  white-space: nowrap;
+}
+
+.radar-control__playback {
+  display: flex;
+  align-items: center;
+  gap: 6px;
+}
+
+.radar-control__playback[hidden] {
+  display: none;
+}
+
+.radar-control__play {
+  /* Override maplibregl-ctrl-group's 29x29px square icon-button sizing. */
+  width: auto;
+  height: auto;
+  border: none;
+  background: none;
+  padding: 2px 4px;
+  font-size: 13px;
+  cursor: pointer;
+}
+
+.radar-control__scrub {
+  width: 110px;
+}
+
+.radar-control__time {
+  font-variant-numeric: tabular-nums;
+  white-space: nowrap;
+}