Replace offline basemap pipeline with Planetiler, unify online/offline styling

Offline tiles were built from Protomaps' own basemap schema, needing a
completely separate hand-tuned theme (protomaps-themes-base + OFFLINE_THEME)
from the online Liberty style's ONLINE_STYLE_PATCH — the two could never be
made to match exactly no matter how much either side got tuned (today's
session found and fixed several mismatches: building opacity, park
boundaries, road casings, road widths).

Offline.pmtiles is now built with Planetiler's default OpenMapTiles profile
against Geofabrik per-country OSM extracts (osmium-merged when more than one
country is selected), the same vector schema Liberty already expects.
offlineStyle() now clones the same Liberty JSON (vendored as a local
snapshot for reliability with no internet) and applies the identical
ONLINE_STYLE_PATCH, just repointed at local PMTiles/glyphs/sprite — one
palette instead of two, correct on both sides by construction.

Also vendors Liberty's icon sprite for the first time (offline had none
before), adds Java/osmium-tool/planetiler.jar to the Docker image, and
removes the now-unused protomaps-themes-base dependency and the
theme-comparison debug page that found today's bugs.

docs/nps-resources.adoc

@@ -24,8 +24,8 @@ checking here before searching from zero next time.
 | MIT (per `package.json`); the whole `npmap5-plugins` repo is separately
   public domain as a US government work
 
-| Park Tiles color palette (offline + online basemap themes)
-| `public/js/map.js`'s `OFFLINE_THEME` and `ONLINE_STYLE_PATCH`
+| Park Tiles color palette (shared offline + online basemap theme)
+| `public/js/map.js`'s `ONLINE_STYLE_PATCH`
 | Colors only — see <<park-tiles>> for why the actual tile service isn't used
 
 | `overview` (top-right minimap/inset control)
@@ -187,7 +187,7 @@ why this app uses OpenFreeMap Liberty as its actual basemap, not Park
 Tiles — see `docs/architecture.adoc`'s "Offline maps" section.
 
 Recreating the *color choices* is a different matter — not the kind of
-thing a data license restricts — and is what `OFFLINE_THEME` in
+thing a data license restricts — and is what `ONLINE_STYLE_PATCH` in
 `public/js/map.js` actually does (see `docs/architecture.adoc`).
 
 === Public style JSON (source for the real colors we did pull)
@@ -219,11 +219,11 @@ embedded credentials, even when technically reachable:
 |===
 
 Colors actually pulled from the Imagery style JSON and used in
-`OFFLINE_THEME`: background (`hsl(40, 37%, 97%)`, a warm cream), the
+`ONLINE_STYLE_PATCH`: background (`hsl(40, 37%, 97%)`, a warm cream), the
 park/protected-area green (`#b3e378`), the two road-importance tiers
 (`#fdefbe`/`#fef7dd`), and the park-boundary line color (`#546619`, dark
-olive). The rest of `OFFLINE_THEME` extends that same warm/olive family
-by eye rather than from a sourced value.
+olive). The rest of `ONLINE_STYLE_PATCH` extends that same warm/olive
+family by eye rather than from a sourced value.
 
 === Legend / cartographic hierarchy