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_en.arb

@@ -116,6 +116,8 @@
   "workoutElevationChart": "Elevation",
   "workoutMapSource": "Map by {name}: it sees your device's address and the area shown, not your track.",
   "@workoutMapSource": {"description": "Under a workout's map: what the map's source sees.", "placeholders": {"name": {"type": "String", "example": "OpenFreeMap"}}},
+  "workoutMapOwn": "Map by your instance, {name}, from OpenStreetMap: it keeps nothing of the area shown.",
+  "@workoutMapOwn": {"description": "Under a workout's map drawn from the instance's own tiles (D50): what it sees.", "placeholders": {"name": {"type": "String", "example": "train.halkyon.eu"}}},
   "workoutMapSourceAbout": "What {name} keeps",
   "@workoutMapSourceAbout": {"description": "A link to the map source's page about what it keeps.", "placeholders": {"name": {"type": "String", "example": "OpenFreeMap"}}},
   "workoutMapUnavailable": "The map can't be loaded now.",