feat(train): Halkyon Train's shell, Todo's copied and renamed (ADR 0030, D12)

apps/train with halkyon_train_server, _client and _flutter, as Todo's:
halkyon_base configured by trainBase(), its own register alone and a
member of the instance's where the operator names one, the app on
halkyon_app's gates with Train's frame, account sheet and About, texts
in British English and German that speak of workouts, app.halkyon.train
on Android, iOS, Linux, macOS and Windows.

Where it differs from Todo: development ports of its own (8180 to 8190),
so it runs beside Learn's server; one initial migration with the schema
Todo's migrations end at (the same tables, compared line by line), not
Todo's seventeen; and Todo's icon as a placeholder until the icon tool
of ADR 0031 draws Train's bike. The workspace, the licences, the READMEs
and AGENTS.md name it.

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/ios/Runner/Assets.xcassets/LaunchImage.imageset/Contents.json

@@ -0,0 +1,23 @@
+{
+  "images" : [
+    {
+      "idiom" : "universal",
+      "filename" : "LaunchImage.png",
+      "scale" : "1x"
+    },
+    {
+      "idiom" : "universal",
+      "filename" : "LaunchImage@2x.png",
+      "scale" : "2x"
+    },
+    {
+      "idiom" : "universal",
+      "filename" : "LaunchImage@3x.png",
+      "scale" : "3x"
+    }
+  ],
+  "info" : {
+    "version" : 1,
+    "author" : "xcode"
+  }
+}

apps/train/halkyon_train_flutter/ios/Runner/Assets.xcassets/LaunchImage.imageset/README.md

@@ -0,0 +1,5 @@
+# Launch Screen Assets
+
+You can customize the launch screen with your own desired assets by replacing the image files in this directory.
+
+You can also do it by opening your Flutter project's Xcode project with `open ios/Runner.xcworkspace`, selecting `Runner/Assets.xcassets` in the Project Navigator and dropping in the desired images.