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_en.arb

@@ -513,6 +513,17 @@
   "@routeDescent": {"placeholders": {"metres": {"type": "int"}}},
   "routeSummary": "{distance} · {ascent}",
   "@routeSummary": {"description": "A route in the list: its distance and climb.", "placeholders": {"distance": {"type": "String", "example": "12.3 km"}, "ascent": {"type": "String", "example": "120 m up"}}},
+  "routesBringIn": "Bring in a GPX file",
+  "@routesBringIn": {"description": "In the Routes tab: a route brought in from a GPX file (ADR 0030, D45)."},
+  "routeBringInTitle": "Bring in {name}",
+  "@routeBringInTitle": {"placeholders": {"name": {"type": "String", "example": "Isar loop"}}},
+  "routeBringInSnap": "Plan it along the paths",
+  "routeBringInSnapHint": "Through its points, with the profile you choose; its turns told",
+  "routeBringInDrawn": "Keep it as drawn",
+  "routeBringInDrawnHint": "Its way as the file has it, no turns told",
+  "routeNotGpx": "This file holds no route Train can read",
+  "routeShareGpx": "Share as GPX",
+  "routeSaveGpx": "Save as GPX",
   "routeOffline": "Keep the map offline",
   "@routeOffline": {"description": "A switch on a saved route: its map kept on this device (ADR 0030, D45)."},
   "routeOfflineOff": "Its map along the way, 2 km either side, on this device for when there's no network",