feat(ui): tabs folding into the title, in Learn's and Train's Profile (ADR 0030, D60)

halkyon_ui's FoldingTabs: the tab row under the app bar's title at the
top, scrolling away with the content, the chosen tab's name then small
under the title, which, tapped, scrolls back up to the row, as Strava's.
Learn's Profile (Profile, Statistics) is built on it, and Train's
Profile in tabs: Progress (your body, the last 12 weeks, this year),
Days, and Plans where the device doesn't record.

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

@@ -249,6 +249,7 @@
   "loopFormIntro": "Dein Band braucht diese Angaben. Sie bleiben in „Dein Körper“, mit deinem Schlüssel versiegelt. Für einen Ruhe- oder Maximalpuls oder eine VO2max, die du nicht angegeben hast, nimmt das Band Polars Standardwerte, und „Dein Körper“ bleibt, wie er ist.",
   "loopFormSave": "Band einrichten",
   "homeWorkouts": "Workouts",
+  "profileTabProgress": "Fortschritt",
   "homeDays": "Tage",
   "homePlans": "Pläne",
   "plansNew": "Neuer Plan",

apps/train/halkyon_train_flutter/lib/l10n/app_en.arb

@@ -312,6 +312,7 @@
   "loopFormIntro": "Your band needs these. They're kept in Your body, sealed with your key. For a resting or highest heart rate or a VO2max you haven't given, the band takes Polar's defaults, and Your body stays as it is.",
   "loopFormSave": "Set up the band",
   "homeWorkouts": "Workouts",
+  "profileTabProgress": "Progress",
   "homeDays": "Days",
   "homePlans": "Plans",
   "plansNew": "New plan",

apps/train/halkyon_train_flutter/lib/l10n/app_localizations.dart

@@ -1516,6 +1516,12 @@ abstract class AppLocalizations {
   /// **'Workouts'**
   String get homeWorkouts;
 
+  /// No description provided for @profileTabProgress.
+  ///
+  /// In en, this message translates to:
+  /// **'Progress'**
+  String get profileTabProgress;
+
   /// No description provided for @homeDays.
   ///
   /// In en, this message translates to:

apps/train/halkyon_train_flutter/lib/l10n/app_localizations_de.dart

@@ -866,6 +866,9 @@ class AppLocalizationsDe extends AppLocalizations {
   @override
   String get homeWorkouts => 'Workouts';
 
+  @override
+  String get profileTabProgress => 'Fortschritt';
+
   @override
   String get homeDays => 'Tage';
 

apps/train/halkyon_train_flutter/lib/l10n/app_localizations_en.dart

@@ -860,6 +860,9 @@ class AppLocalizationsEn extends AppLocalizations {
   @override
   String get homeWorkouts => 'Workouts';
 
+  @override
+  String get profileTabProgress => 'Progress';
+
   @override
   String get homeDays => 'Days';