feat(pdf): cards beside a PDF are written in the composer's own editor

The sidebar wrote a front and a back only. It now holds the composer's
editor with a bloc of its own: every kind of card (multiple choice,
vocabulary with Look up, matching, a map, a character), tags, hints and
the explanation, pinning, duplicating and deleting. A new card is tied
to the page shown, which it can be moved to the current one, and waits
for its chapter's tag by name until it is created; text sent from the
pages goes into its front or its answer, as its kind keeps one. Create
saves it once it is complete, as the composer does; going back asks
before discarding what was written.

The screenshot of the pages has a button at the end of the format bar,
outside its scrolling, where an editor's place is for it
(InsertableBlock.inFormatBar); the Insert menu still lists it.

A new card no longer shows twice in the composer when its stored copy
arrives while it is saved.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MMm7usAo6q9ZZRoPkWjoxi
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

halkyon_learn_flutter/test/feature/card/bloc/card_composer_bloc_test.dart

@@ -595,4 +595,101 @@ void main() {
     expect(await cards.cardsOf('japanese'), isEmpty);
     expect(gateway.deletions, ['blank $neko', 'delete $neko']);
   });
+
+  test('a card written from a PDF knows its page, waits for its chapter '
+      'tag by name, and takes text sent to its front and answer', () async {
+    start();
+    await loaded();
+
+    bloc
+      ..add(
+        const CardComposerEventDraftAdded(
+          'new',
+          source: (pdfId: 'grammar', page: 5),
+          tagNames: ['Particles'],
+        ),
+      )
+      ..add(
+        const CardComposerEventTextAdded(
+          'new',
+          text: 'は marks',
+          toAnswer: false,
+        ),
+      )
+      ..add(
+        const CardComposerEventTextAdded(
+          'new',
+          text: 'the topic',
+          toAnswer: true,
+        ),
+      );
+    final draft = (await until(
+      (s) => s.byId('new')?.content.back.plainText == 'the topic',
+    )).byId('new')!;
+    expect(draft.content.front.plainText, 'は marks');
+    expect(draft.content.source, (pdfId: 'grammar', page: 5));
+    expect(draft.newTagNames, ['Particles']);
+
+    bloc.add(const CardComposerEventLeft('new'));
+    final saved = await until(
+      (s) => s.byId('new')?.status == CardDraftStatus.saved,
+    );
+    final stored = (await cards.cardsOf('japanese')).single;
+    expect(stored.content.source, (pdfId: 'grammar', page: 5));
+    expect((await tags.read()).of(stored.id).single.name, 'Particles');
+    // Held by its draft alone, never also among the stored cards.
+    expect(saved.items.where((d) => d.cardId == stored.id), hasLength(1));
+  });
+
+  test('text for the answer goes where the kind of card keeps it', () {
+    final base = card('猫', '');
+    expect(
+      base.withTextAdded('cat', toAnswer: true).back.plainText,
+      'cat',
+    );
+    final word = CardContent(
+      front: text('猫'),
+      back: RichContent.empty(),
+      type: CardType.vocabulary,
+      meanings: const ['cat'],
+    );
+    expect(
+      word.withTextAdded('feline\nanimal', toAnswer: true).meanings,
+      ['cat', 'feline animal'],
+    );
+    final choice = CardContent(
+      front: text('猫'),
+      back: RichContent.empty(),
+      type: CardType.multipleChoice,
+      answers: [
+        CardAnswer(content: text('dog')),
+        CardAnswer(content: RichContent.empty(), correct: true),
+      ],
+    );
+    expect(
+      choice.withTextAdded('cat', toAnswer: true).answers[1].content.plainText,
+      'cat',
+    );
+  });
+
+  test('discarding drops a new card, and takes a stored one back to how '
+      'it is stored', () async {
+    final neko = await cards.create('japanese', card('猫', 'cat'));
+    start();
+    await loaded();
+
+    bloc
+      ..add(const CardComposerEventDraftAdded('new'))
+      ..add(CardComposerEventChanged(neko, card('猫', 'kitten')))
+      ..add(const CardComposerEventDiscarded('new'))
+      ..add(CardComposerEventDiscarded(neko));
+    final state = await until(
+      (s) =>
+          s.byId('new') == null &&
+          s.byId(neko)?.content.back.plainText == 'cat',
+    );
+
+    expect(state.byId(neko)!.isDirty, isFalse);
+    expect(await cards.cardsOf('japanese'), hasLength(1));
+  });
 }