fix(app): Reorder among older items, export and text import that hold up

- Reorder: rows from before an order existed all share one position, and
  one moved among them landed at their end; the run it goes into now
  gets positions of its own (placeAmong), for notes, files, paths,
  steps and sub-studysets. Rows whose deletion can still be undone count
  for nothing, as the list leaves them out, and a dropped row takes its
  place at once instead of snapping back until the order is read again.
- Export: two studysets inside each other (moved so on two devices
  offline) no longer make it run forever; links to files whose names
  hold #, % or brackets work; PDFs, images and sounds go into the zip
  without being compressed again; any error says the export failed.
- Text import: a real CSV reader (quoted fields over several lines, a
  back over several quoted fields, a stray quote spoiling only its own
  line), the separator guessed from the text (semicolons from German
  spreadsheets), and files in UTF-16 or Windows-1252 read as meant.
- A tab whose notes, paths or files couldn't be read says so rather than
  "No … yet"; an Anki import from the Library that fails leaves no empty
  studyset behind.

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/model/card_text_import_test.dart

@@ -1,3 +1,5 @@
+import 'dart:convert';
+
 import 'package:flutter_test/flutter_test.dart';
 import 'package:halkyon_learn_flutter/src/feature/card/model/card_text_import.dart';
 
@@ -61,4 +63,59 @@ void main() {
     expect(CardSeparator.forFile('words.tsv'), CardSeparator.tab);
     expect(CardSeparator.forFile('words.txt'), CardSeparator.tab);
   });
+
+  test('a quoted field may run over several lines, and a back over '
+      'several fields keeps none of their quotes', () {
+    expect(
+      parseCardLines(
+        '"word","line one\nline two"\n"a","b","c"\nnext,one',
+        CardSeparator.comma,
+      ),
+      [
+        (front: 'word', back: 'line one\nline two'),
+        (front: 'a', back: 'b,c'),
+        (front: 'next', back: 'one'),
+      ],
+    );
+  });
+
+  test('a quote that never closes spoils only its own line', () {
+    expect(
+      parseCardLines('"hello,hola\nsí,yes', CardSeparator.comma),
+      [(front: 'sí', back: 'yes')],
+    );
+  });
+
+  test('the separator is guessed from what the lines hold: semicolons as '
+      'German spreadsheets write them, whatever the name', () {
+    expect(
+      guessSeparator(
+        'Wort;Bedeutung, mit Komma\nHaus;house',
+        fileName: 'w.csv',
+      ),
+      CardSeparator.semicolon,
+    );
+    expect(
+      guessSeparator('hola\thello, hi\nsí\tyes', fileName: 'w.csv'),
+      CardSeparator.tab,
+    );
+    expect(
+      guessSeparator('nothing here', fileName: 'w.csv'),
+      CardSeparator.comma,
+    );
+  });
+
+  test('a file is read in whichever encoding it was saved: UTF-8, UTF-16 '
+      'with its mark, or Windows-1252', () {
+    expect(decodeCardText(utf8.encode('Straße;street')), 'Straße;street');
+    expect(
+      decodeCardText([0xFF, 0xFE, 0x68, 0, 0x3B, 0, 0x42, 0x30]),
+      'h;あ',
+    );
+    // "Café – €" as Windows-1252.
+    expect(
+      decodeCardText([0x43, 0x61, 0x66, 0xE9, 0x20, 0x96, 0x20, 0x80]),
+      'Café – €',
+    );
+  });
 }

halkyon_learn_flutter/test/feature/card/widget/card_text_import_test.dart

@@ -128,14 +128,46 @@ void main() {
     expect(await stored(), [('hello, friend', 'hola amigo')]);
   });
 
-  testWidgets("a file that isn't UTF-8 text says so", (tester) async {
+  testWidgets('a file that holds no text says so', (tester) async {
     await showApp(tester);
     await openImport(tester);
-    files.next = (name: 'words.csv', bytes: Uint8List.fromList([0xff, 0xfe]));
+    files.next = (
+      name: 'words.csv',
+      bytes: Uint8List.fromList([0x89, 0x50, 0x4E, 0x47, 0x00, 0x00, 0x1A]),
+    );
 
     await tester.tap(find.text('Load a CSV or TSV file'));
     await tester.pumpAndSettle();
 
-    expect(find.text("This file isn't text in UTF-8."), findsOneWidget);
+    expect(find.text("This file doesn't hold text."), findsOneWidget);
+  });
+
+  testWidgets('a file an older spreadsheet saved (Windows-1252, semicolons) '
+      'is read as it is meant', (tester) async {
+    await showApp(tester);
+    await openImport(tester);
+    // "Café;coffee" as Windows-1252.
+    files.next = (
+      name: 'words.csv',
+      bytes: Uint8List.fromList([
+        0x43,
+        0x61,
+        0x66,
+        0xE9,
+        0x3B,
+        0x63,
+        0x6F,
+        0x66,
+        0x66,
+        0x65,
+        0x65,
+      ]),
+    );
+
+    await tester.tap(find.text('Load a CSV or TSV file'));
+    await tester.pumpAndSettle();
+
+    expect(find.widgetWithText(TextField, 'Café;coffee'), findsOneWidget);
+    expect(find.text('1 card ready to import.'), findsOneWidget);
   });
 }