Add a Home button and fill icon gaps from NPS's newer symbol library

Two things pulled in from github.com/nationalparkservice/npmap5-plugins:

- A "Home" button (public/vendor/npmap-home-button/, NPS's own MapLibre
  control) pinned to the app's CENTER/ZOOM, sitting top-left on the map. Now
  that the URL hash permalink can open the map at any view, "current view"
  and "the default view" aren't the same thing anymore, so a quick way back
  to the default is worth having.

- npmap5-plugins bundles a newer, actively-maintained version of the same
  NPS symbol-library already used for POI_ICONS (confirmed by its
  maintainer to be the designated replacement for the older standalone
  repo: nationalparkservice/npmap5-plugins#4), with a much larger icon
  vocabulary and a simpler CC0 (public domain) license. All 25 icons
  already in use came back byte-identical from the new source, so this
  just repoints their attribution — but it also has icons the old repo
  didn't: `forest` (POI_ICONS) is now the official "wilderness" pictogram
  instead of hand-drawn, and three of the five previously icon-less
  Services/Activities tags (wifi, mobile data coverage, winter/snow
  camping) now have real icons too. Only bakery and vehicle wash still
  have no NPS equivalent.

docs/architecture.adoc

@@ -117,6 +117,14 @@ Maps use, so copying the URL bar shares the exact spot someone's
 looking at, and reloading the page doesn't reset the view back to the
 default.
 
+Now that any view can be the starting one (via that permalink), a way
+back to the app's actual default is worth having: a "Home" button
+(`public/vendor/npmap-home-button/`, the National Park Service's own
+`home-button` MapLibre control — see `docs/third-party-notices.adoc`)
+sits top-left on the map, pinned to `CENTER`/`ZOOM` explicitly rather
+than its own fallback (the view at construction time, which would just
+be wherever a loaded permalink happened to point).
+
 == Weather radar overlay
 
 `public/js/radar.js` adds a "Radar" map control that overlays recent
@@ -252,13 +260,14 @@ categories p4n2gpx actually uses, not an exhaustive OsmAnd icon set)
 draws a white glyph on top of the badge for any waypoint whose `icon`
 matches a known key (filtered out entirely for anything else, so an
 unrecognized icon key just falls back to a plain colored badge rather
-than a broken/missing image warning). Six of the seven glyphs are the
-National Park Service's own map symbols
-(`github.com/nationalparkservice/symbol-library`, BSD-licensed,
-originally forked from Mapbox's Maki project) — a professional,
+than a broken/missing image warning). All seven glyphs are the National
+Park Service's own map symbols — pulled from
+`github.com/nationalparkservice/npmap5-plugins`'s bundled
+`symbol-library` (CC0-licensed, an actively-maintained monorepo that's
+the designated replacement for the same org's older standalone
+`symbol-library` repo, per its maintainer) — a professional,
 purpose-built icon set beats hand-drawing "fuel pump"/"picnic table"
-glyphs from scratch; `forest` has no NPS equivalent (that set covers
-facilities, not land cover) and stays hand-drawn.
+glyphs from scratch.
 +
 Both the badge and the glyphs are rasterized from their source SVGs
 (an `<img>` → `<canvas>` → `ImageData` round trip, since `map.addImage`
@@ -366,10 +375,11 @@ instead. That table covers the codes p4n2gpx's exports actually use
 (not park4night's whole API), with a human label always and an icon
 only where the icon set below has a reasonable match — most of the
 icons are National Park Service symbols again (same source/license as
-`POI_ICONS`), a few (bakery, wifi, vehicle wash, ...) have no NPS
-equivalent and get a label with no icon. A code this table doesn't
-cover at all just renders as its own raw text, same as before this
-existed — nothing p4n2gpx might add later is silently dropped.
+`POI_ICONS`); a couple (bakery, vehicle wash) have no NPS equivalent
+even in that larger set and get a label with no icon. A code this
+table doesn't cover at all just renders as its own raw text, same as
+before this existed — nothing p4n2gpx might add later is silently
+dropped.
 
 Track properties:: Every track feature (both formats) also carries
 `distance_meters`, `elevation_gain_meters`, `duration_secs`,