A logged-in user can now trigger, from a new "Offline data" sidebar
panel, what was previously a fully manual go-pmtiles workflow
(docs/development.adoc): regenerate either file for the current map
viewport, no area-picker (same "visible area is the area" convention
the Overpass POI plugin already uses).
- lib/maptool/pmtiles_builder.rb: two independent background jobs
(Thread + Mutex-guarded status Hash, same shape as app.rb's own GNSS
poller), each writing to a .tmp path and atomically renaming into
place so a build never serves a partially-written file mid-run.
offline.pmtiles is a single `pmtiles extract` against Protomaps'
public daily basemap build (byte-range extraction, not a full
~120GB download). terrain.pmtiles has no equivalent public
Terrarium-encoded archive to extract from, so it fetches individual
Terrarium tiles itself, packs them into an intermediate MBTiles
(new sqlite3 gem), then the same `pmtiles convert`.
- 4 new app.rb routes (POST .../build, GET .../build-status) plus
size/mtime added to the existing availability endpoints.
- public/js/offline_data.js: new sidebar panel, polling build-status
the same self-rescheduling-setTimeout shape livetrack.js already
uses for its own refresh loop.
- Both network-heavy pieces (the Protomaps build index, per-tile
fetches) are injectable, so test/test_pmtiles_builder.rb exercises
the actual build pipeline against a fake `pmtiles` binary without
hitting a real network, matching this suite's existing
keep-it-offline convention for external services.
