fix(app): glyph shapes, languages, licences and the side bar's foot

- A Japanese front keeps Japanese shapes whatever the back's language
  (Japanese learnt in Chinese or Korean took Chinese or Korean shapes).
- A change of languages no longer rebuilds the screen below: the scope
  keeps one shape, so a study session keeps its Undo.
- The PDF reader, with the cards and notes written beside it, takes its
  studyset's languages too.
- Licences: GPL-3.0 and AGPL-3.0 mean "only", as SPDX defines them (not
  "or later"); GPLv3 and "public domain" stay as typed; words around a
  Creative Commons licence ("International", "Unported", "Deed") and its
  name written out are read; 4.0 takes no jurisdiction.
- A new sub-studyset takes its parent's licence, not its holder or year.
- The year says it is wrong once typed whole or left; full-width digits
  count; the year's range comes from clock.
- New sub-studyset shows whole in the side bar, no longer cut at half.
- The languages switch says that neither side set means inheriting;
  "license" as the British verb.

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/lib/l10n/app_localizations_de.dart

@@ -1139,7 +1139,7 @@ class AppLocalizationsDe extends AppLocalizations {
 
   @override
   String get studysetSheetLanguagesInherited =>
-      'Ausgeschaltet übernimmt es die Sprachen des Lernsets, in dem es liegt.';
+      'Ausgeschaltet oder ohne festgelegte Seite übernimmt es die Sprachen des Lernsets, in dem es liegt.';
 
   @override
   String get studysetSheetFrontLanguage => 'Sprache der Vorderseite';