feat(jellyfin): any stretch of a line's characters chosen by hand

The cut takes the longest word and knows no grammar, so 今日は reads as
こんにちは where it is 今日 and は. Any stretch of a line's characters can
now be chosen by hand: dragged across with a mouse, Shift+clicked from
the word or stretch chosen, or on a touch screen held on a character and
dragged on. It is looked up as one word, as it stands or as a form of
one, in one small request (the instance has the line's text already);
while it is chosen the line reads it as that word (きょう over 今日), and
what the dictionary lacks as one word is offered as a search on Jisho.

The line's words move into line_words.dart, out of the Watch screen.

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/test/feature/jellyfin/watch_screen_test.dart

@@ -600,6 +600,98 @@ void main() {
     expect(card.content.entry, (source: 'jmdict', id: '37'));
   });
 
+  group('a stretch chosen by hand (decided 2026-10-13: by characters)', () {
+    final greetings = [
+      word('40', '今日', reading: 'きょう', pos: ['n'], glosses: ['today']),
+      word('41', '今日は', reading: 'こんにちは', pos: ['int'], glosses: ['hello']),
+      word('42', 'は', pos: ['prt'], labels: ['common']),
+      word('43', '雨', reading: 'あめ', pos: ['n'], glosses: ['rain']),
+      word('44', 'だ', pos: ['cop'], labels: ['common']),
+    ];
+    Future<void> watchGreetings(WidgetTester tester) async {
+      await watch(
+        tester,
+        vtt: {
+          ('episode-1', 2): 'WEBVTT\n\n00:00:01.000 --> 00:00:05.000\n今日は雨だ\n',
+          ('episode-1', 3):
+              'WEBVTT\n\n00:00:01.000 --> 00:00:05.000\nA grey sky.\n',
+        },
+        words: greetings,
+      );
+      await playTo(tester, const Duration(seconds: 2));
+    }
+
+    /// The middle of the [index]th character of the base text [text] of
+    /// the line (four characters to a run at most here, each as wide).
+    Offset character(WidgetTester tester, String text, int index) {
+      final rect = tester.getRect(find.text(text, findRichText: true).first);
+      final width = rect.width / text.length;
+      return Offset(rect.left + width * (index + 0.5), rect.center.dy);
+    }
+
+    testWidgets('dragged across with a mouse, the characters chosen are '
+        'looked up as one word, also inside a word the cut took longer: '
+        '今日 out of 今日は', (tester) async {
+      await watchGreetings(tester);
+      await players.last!.play();
+      expect(find.text('今日', findRichText: true), findsOneWidget);
+
+      final drag = await tester.startGesture(
+        character(tester, '今日', 0),
+        kind: PointerDeviceKind.mouse,
+      );
+      await drag.moveTo(character(tester, '今日', 1));
+      await drag.up();
+      await tester.pumpAndSettle();
+
+      expect(players.last!.state.value.playing, isFalse);
+      expect(find.textContaining('today', findRichText: true), findsOneWidget);
+      expect(find.textContaining('hello', findRichText: true), findsNothing);
+      // While chosen, the line reads it as the word chosen: きょう, not
+      // こんにち of こんにちは.
+      expect(find.text('こんにち'), findsNothing);
+      expect(find.text('きょう'), findsWidgets);
+    });
+
+    testWidgets('Shift+click chooses from the word chosen to the character '
+        'clicked; what the dictionary lacks as one word is searched on '
+        'Jisho', (tester) async {
+      await watchGreetings(tester);
+      await tester.tap(find.text('雨', findRichText: true));
+      await tester.pumpAndSettle();
+      expect(find.textContaining('rain', findRichText: true), findsOneWidget);
+
+      await tester.sendKeyDownEvent(LogicalKeyboardKey.shiftLeft);
+      final click = await tester.startGesture(
+        character(tester, 'だ', 0),
+        kind: PointerDeviceKind.mouse,
+      );
+      await click.up();
+      await tester.sendKeyUpEvent(LogicalKeyboardKey.shiftLeft);
+      await tester.pumpAndSettle();
+
+      expect(
+        find.text("雨だ isn't in the dictionary as one word."),
+        findsOneWidget,
+      );
+      expect(find.text('Search Jisho for it'), findsOneWidget);
+      expect(find.textContaining('rain', findRichText: true), findsNothing);
+    });
+
+    testWidgets('on a phone, holding a character starts a stretch, and '
+        'moving on extends it', (tester) async {
+      await watchGreetings(tester);
+
+      final hold = await tester.startGesture(character(tester, '今日', 0));
+      await tester.pump(const Duration(milliseconds: 600));
+      await hold.moveTo(character(tester, '今日', 1));
+      await hold.up();
+      await tester.pumpAndSettle();
+
+      expect(find.textContaining('today', findRichText: true), findsOneWidget);
+    });
+  });
+
   testWidgets("the episode's words can be studied or crammed: the cards of "
       'its words, held before it was watched too, get its tag', (tester) async {
     final station = sampleWords.firstWhere((word) => word.headword == '駅');