feat(app): study with faces on the ratings, centred cards and the session's figures

The study session, reworked:

- Ratings are coloured tiles with a face each (frown, meh, smile,
  laugh), when the card comes back below them with a clock ("in 1
  min", "in 3 days"), always shown, so a card can be rated without
  revealing it; at most 540 dp wide, centred.
- Cards are centred in a section card: the question large, then a line
  with 24 dp on either side and the answer a size smaller, or "Show
  answer" 40 dp below; a tap anywhere on the card shows or hides the
  answer. Read-only rich text takes a text style and an alignment.
- Words show their reading small above the expression once answered,
  and several meanings numbered.
- Choice, matching and map cards: Check below the card, the ratings in
  its place once checked; options marked before their text; matching
  lists the categories first, then what is left to place; the map
  fills the card with one caption below it.
- Header and progress on a band of their own; title start-aligned,
  the Pomodoro timer only to watch, the back-first toggle in every
  state; leaving a round under way asks first.
- Cramming goes round the round; back is there with two cards or more,
  skipping always.
- The end of a round: the cards done of those due, accuracy (OK counts
  half) and time, over the whole session.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

halkyon_learn_flutter/lib/l10n/app_localizations_en.dart

@@ -1516,6 +1516,47 @@ class AppLocalizationsEn extends AppLocalizations {
   @override
   String get studyCheck => 'Check';
 
+  @override
+  String get studySelectAll => 'Select all that apply';
+
+  @override
+  String get studySelectOne => 'Select the correct answer';
+
+  @override
+  String get studyMatchingInstructions => 'DRAG AND DROP ONTO CARDS ABOVE';
+
+  @override
+  String get studyMatchingAllPlaced => 'All placed';
+
+  @override
+  String get studyMatchingDropHere => 'Drop here';
+
+  @override
+  String get studyMapTapPrompt => 'Tap a region to answer';
+
+  @override
+  String studyMapSelected(String label) {
+    return 'Selected: $label';
+  }
+
+  @override
+  String get studyCorrect => 'Correct';
+
+  @override
+  String studyCorrectLabel(String label) {
+    return 'Correct — $label';
+  }
+
+  @override
+  String studyMapAnswer(String answer) {
+    return 'Answer: $answer';
+  }
+
+  @override
+  String studyMapPickedAnswer(String picked, String answer) {
+    return 'You picked $picked · Answer: $answer';
+  }
+
   @override
   String get studyRatingBad => 'Bad';
 
@@ -1543,7 +1584,129 @@ class AppLocalizationsEn extends AppLocalizations {
   String get studyDone => 'Done';
 
   @override
-  String get studyRoundDone => 'Round complete';
+  String get studySessionComplete => 'Session complete';
+
+  @override
+  String studyProgressReviewed(int reviewed, int total) {
+    return '$reviewed / $total reviewed';
+  }
+
+  @override
+  String studyReviewedCount(int reviewed) {
+    return '$reviewed reviewed';
+  }
+
+  @override
+  String get studyStatCards => 'Cards';
+
+  @override
+  String get studyStatAccuracy => 'Accuracy';
+
+  @override
+  String get studyStatTime => 'Time';
+
+  @override
+  String studyDurationSec(int sec) {
+    return '$sec sec';
+  }
+
+  @override
+  String studyDurationMin(int min) {
+    return '$min min';
+  }
+
+  @override
+  String studyDurationMinSec(int min, int sec) {
+    return '$min min $sec sec';
+  }
+
+  @override
+  String get studyLeaveTitle => 'Leave this study session?';
+
+  @override
+  String studyLeaveRated(int count) {
+    String _temp0 = intl.Intl.pluralLogic(
+      count,
+      locale: localeName,
+      other:
+          'Your ratings so far are saved, but the $count cards still left in this round will be discarded if you leave now.',
+      one: 'Your ratings so far are saved, but the last card in this round will be discarded if you leave now.',
+    );
+    return '$_temp0';
+  }
+
+  @override
+  String studyLeaveUnrated(int count) {
+    String _temp0 = intl.Intl.pluralLogic(
+      count,
+      locale: localeName,
+      other:
+          'You haven’t rated any of the $count cards in this round yet — leaving ends the session without recording any progress for it.',
+      one: 'You haven’t rated this card yet — leaving ends the session without recording any progress for this round.',
+    );
+    return '$_temp0';
+  }
+
+  @override
+  String get studyLeaveConfirm => 'Leave';
+
+  @override
+  String get studyKeepStudying => 'Keep studying';
+
+  @override
+  String studyInMinutes(int count) {
+    String _temp0 = intl.Intl.pluralLogic(
+      count,
+      locale: localeName,
+      other: 'in $count min',
+      one: 'in 1 min',
+    );
+    return '$_temp0';
+  }
+
+  @override
+  String studyInHours(int count) {
+    String _temp0 = intl.Intl.pluralLogic(
+      count,
+      locale: localeName,
+      other: 'in $count hours',
+      one: 'in 1 hour',
+    );
+    return '$_temp0';
+  }
+
+  @override
+  String studyInDays(int count) {
+    String _temp0 = intl.Intl.pluralLogic(
+      count,
+      locale: localeName,
+      other: 'in $count days',
+      one: 'in 1 day',
+    );
+    return '$_temp0';
+  }
+
+  @override
+  String studyInMonths(int count) {
+    String _temp0 = intl.Intl.pluralLogic(
+      count,
+      locale: localeName,
+      other: 'in $count months',
+      one: 'in 1 month',
+    );
+    return '$_temp0';
+  }
+
+  @override
+  String studyInYears(int count) {
+    String _temp0 = intl.Intl.pluralLogic(
+      count,
+      locale: localeName,
+      other: 'in $count years',
+      one: 'in 1 year',
+    );
+    return '$_temp0';
+  }
 
   @override
   String get studyContinue => 'Continue learning';
@@ -1552,17 +1715,7 @@ class AppLocalizationsEn extends AppLocalizations {
   String get studyPrevious => 'Previous card';
 
   @override
-  String get studyNext => 'Next card';
-
-  @override
-  String get studyReading => 'Reading';
-
-  @override
-  String get studyMeanings => 'Meanings';
-
-  @override
-  String get studyPlaceItems =>
-      'Drag each item onto its category, or tap an item and then a category.';
+  String get studySkipCard => 'Skip card';
 
   @override
   String studyMinutes(int count) {