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/macos/Flutter/Flutter-Debug.xcconfig

@@ -0,0 +1 @@
+#include "ephemeral/Flutter-Generated.xcconfig"

apps/train/halkyon_train_flutter/macos/Flutter/Flutter-Release.xcconfig

@@ -0,0 +1 @@
+#include "ephemeral/Flutter-Generated.xcconfig"

apps/train/halkyon_train_flutter/macos/Flutter/GeneratedPluginRegistrant.swift

@@ -0,0 +1,30 @@
+//
+//  Generated file. Do not edit.
+//
+
+import FlutterMacOS
+import Foundation
+
+import connectivity_plus
+import desktop_webview_window
+import file_picker_darwin
+import file_selector_macos
+import flutter_secure_storage_darwin
+import flutter_web_auth_2
+import google_sign_in_ios
+import sign_in_with_apple
+import url_launcher_macos
+import window_to_front
+
+func RegisterGeneratedPlugins(registry: FlutterPluginRegistry) {
+  ConnectivityPlusPlugin.register(with: registry.registrar(forPlugin: "ConnectivityPlusPlugin"))
+  DesktopWebviewWindowPlugin.register(with: registry.registrar(forPlugin: "DesktopWebviewWindowPlugin"))
+  FilePickerPlugin.register(with: registry.registrar(forPlugin: "FilePickerPlugin"))
+  FileSelectorPlugin.register(with: registry.registrar(forPlugin: "FileSelectorPlugin"))
+  FlutterSecureStorageDarwinPlugin.register(with: registry.registrar(forPlugin: "FlutterSecureStorageDarwinPlugin"))
+  FlutterWebAuth2Plugin.register(with: registry.registrar(forPlugin: "FlutterWebAuth2Plugin"))
+  GoogleSignInPlugin.register(with: registry.registrar(forPlugin: "GoogleSignInPlugin"))
+  SignInWithApplePlugin.register(with: registry.registrar(forPlugin: "SignInWithApplePlugin"))
+  UrlLauncherPlugin.register(with: registry.registrar(forPlugin: "UrlLauncherPlugin"))
+  WindowToFrontPlugin.register(with: registry.registrar(forPlugin: "WindowToFrontPlugin"))
+}