feat(train): routes out and in as GPX (ADR 0030, D45)

A route's page shares it as GPX 1.1 (Android's share sheet, else saved
where the person chooses): its way a track with elevations, its
waypoints and turns as named points. A GPX file comes in from the Routes
tab or, on Android, opened with Train or shared to it; it is planned
along the paths through its points or kept as drawn, then named and
saved as a new route.

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

@@ -405,6 +405,15 @@
   "routeAscent": "{metres} m bergauf",
   "routeDescent": "{metres} m bergab",
   "routeSummary": "{distance} · {ascent}",
+  "routesBringIn": "GPX-Datei hereinholen",
+  "routeBringInTitle": "{name} hereinholen",
+  "routeBringInSnap": "Entlang der Wege planen",
+  "routeBringInSnapHint": "Durch ihre Punkte, mit dem Profil deiner Wahl; ihre Abzweigungen angesagt",
+  "routeBringInDrawn": "So lassen, wie sie ist",
+  "routeBringInDrawnHint": "Ihr Weg, wie ihn die Datei hat, ohne Ansagen",
+  "routeNotGpx": "In dieser Datei steckt keine Route, die Train lesen kann",
+  "routeShareGpx": "Als GPX teilen",
+  "routeSaveGpx": "Als GPX speichern",
   "routeOffline": "Karte offline behalten",
   "routeOfflineOff": "Die Karte entlang des Wegs, 2 km zu beiden Seiten, auf diesem Gerät für unterwegs ohne Netz",
   "routeOfflineLoading": "Karte wird gespeichert: {done} von {total} Kacheln",