feat(learn): the assistant's button folded on Home too, the conversation at full height folding into it, and smaller fixes from the developer's list (ADR 0021, D64, D65)

- Home's assistant starts folded into its button at the lower left, as
  in the Library, where a field stood at its foot.
- The button has Material 3's floating action button shape (a rounded
  square) rather than a circle, its gradient ring kept.
- On a studyset below expanded windows it stands in one row with Add
  material and Study rather than above them.
- While studying, the ratings below the card make way while its field
  is open rather than standing under it.
- The conversation opens at the window's full height, its header above
  the list, so a drag on the header moves the sheet and a drag on the
  list scrolls it. Close ends the conversation; any other way out folds
  it into the button (ConversationDockCubit, above the router), its
  answer still coming, until any button opens it again or another
  conversation starts.
- An answer's Copy icon lines up with the answer's text.
- A sense's grammar notes run on after its glosses as one flowing text,
  so a short note such as "n" no longer takes a line of its own.
- A card's hints show their count in a grey badge beside the title, so
  it no longer reads as the hint's number.

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/learn/halkyon_learn_flutter/test/feature/card/widget/vocabulary_senses_test.dart

@@ -37,7 +37,10 @@ void main() {
     );
 
     expect(find.text('1.'), findsOneWidget);
-    expect(find.text('house; home'), findsOneWidget);
+    expect(
+      find.textContaining('house; home', findRichText: true),
+      findsOneWidget,
+    );
     final tag = tester.widget<Text>(find.text('n,'));
     expect(tag.style?.fontStyle, FontStyle.italic);
     expect(tag.style?.fontSize, 16 * 0.85);
@@ -78,4 +81,41 @@ void main() {
     expect(notes.single.style?.fontStyle, FontStyle.italic);
     expect(notes.single.style?.color, theme.colorScheme.onSurfaceVariant);
   });
+
+  testWidgets("a sense's notes run on after its glosses, never on a line "
+      'of their own while they fit after the last word', (tester) async {
+    tester.view.physicalSize = const Size(300, 600);
+    tester.view.devicePixelRatio = 1;
+    addTearDown(tester.view.reset);
+    await show(
+      tester,
+      const Align(
+        alignment: Alignment.topLeft,
+        child: SizedBox(
+          width: 240,
+          child: VocabularySensesView(
+            senses: [
+              VocabularySense(
+                glosses: ['fondness for alcohol', 'drinker'],
+                pos: ['n'],
+              ),
+            ],
+            style: TextStyle(fontSize: 16),
+            centred: false,
+          ),
+        ),
+      ),
+    );
+
+    final glosses = find.textContaining(
+      'fondness for alcohol; drinker',
+      findRichText: true,
+    );
+    final tag = tester.getRect(find.text('n'));
+    final text = tester.getRect(glosses);
+    // Two lines of glosses: the note on the second, after "drinker".
+    expect(text.height, greaterThan(30));
+    expect(tag.left, greaterThan(text.left + 20));
+    expect(tag.bottom, closeTo(text.bottom, 6));
+  });
 }