feat(train): the instance's own map tiles, drawn by Train's style (ADR 0030, D50)

Protomaps' basemap cut for Europe and served by pmtiles beside Train's server
(compose.maps.yaml), drawn by Train's own style, light and dark, which the
server serves. Only people signed in get tiles: map.source hands a key that
Caddy has the server check before each tile; nothing logs a tile.

Also fixes .dockerignore, which left apps/train/ out of the build context, so
Train's server's and BRouter's images couldn't have been built.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

.gitignore

@@ -29,6 +29,10 @@ deploy/assistants.env
 # A sidecar's files on the server, such as Jellyfin's configuration and media
 deploy/jellyfin/
 deploy/languagetool/
+# BRouter's segments and the map's tiles (Train's ADR 0030, D44, D50), downloaded on
+# an instance
+deploy/brouter/segments/
+deploy/maps/tiles/
 # Dictionary files an instance loads: made by halkyon_learn_curator, not kept in git.
 deploy/dictionaries/*.jsonl
 deploy/dictionaries/*.jsonl.gz