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>

apps/train/halkyon_train_flutter/lib/l10n/app_de.arb

@@ -92,6 +92,7 @@
   "workoutSpeedChart": "Geschwindigkeit",
   "workoutElevationChart": "Höhe",
   "workoutMapSource": "Karte von {name}: sieht die Adresse deines Geräts und den gezeigten Ausschnitt, nicht deine Strecke.",
+  "workoutMapOwn": "Karte von deiner Instanz, {name}, aus OpenStreetMap: sie speichert nichts vom gezeigten Ausschnitt.",
   "workoutMapSourceAbout": "Was {name} speichert",
   "workoutMapUnavailable": "Die Karte kann gerade nicht geladen werden.",
   "workoutNotFound": "Dieses Training gibt es nicht mehr.",