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/vendor/maplibre-gl/maplibre-gl.css

@@ -0,0 +1 @@
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