feat(editor): text above is named by the language, shown on hover or a long press

Furigana was the only name for text set above text, though it carries
pinyin, a pronunciation or a translation as well. Its button and dialog
now say furigana in a Japanese studyset, pinyin in a Chinese one, and
text above elsewhere, each with an example of its own: the studyset's
languages reach the core's editors through ContentLanguages, which the
studyset's language scope now sets.

Read-only, the text above shows only under the pointer or after a long
press (another hides it), so the text can be read without it first; its
room stays, so no line moves. While editing, it shows over the pointer
above its dotted text; with the caret inside such text, the button
selects all of it and edits what it has, so it can be seen and changed
without finding its ends.

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_en.dart

@@ -2863,7 +2863,13 @@ class AppLocalizationsEn extends AppLocalizations {
   String get formatSubscript => 'Subscript';
 
   @override
-  String get formatRuby => 'Furigana (a reading above the text)';
+  String get formatRuby => 'Text above (a pronunciation, a translation)';
+
+  @override
+  String get formatRubyFurigana => 'Furigana (a reading above the text)';
+
+  @override
+  String get formatRubyPinyin => 'Pinyin (above the characters)';
 
   @override
   String get formatLink => 'Link';
@@ -2887,7 +2893,19 @@ class AppLocalizationsEn extends AppLocalizations {
   String get linkRemove => 'Remove link';
 
   @override
-  String get rubyTitle => 'Furigana';
+  String get rubyTitle => 'Text above';
+
+  @override
+  String get rubyTitleFurigana => 'Furigana';
+
+  @override
+  String get rubyTitlePinyin => 'Pinyin';
+
+  @override
+  String get rubyText => 'Text';
+
+  @override
+  String get rubyHint => 'e.g. a pronunciation or a translation';
 
   @override
   String get rubyReading => 'Reading';
@@ -2895,6 +2913,9 @@ class AppLocalizationsEn extends AppLocalizations {
   @override
   String get rubyReadingHint => 'In kana, e.g. かんじ';
 
+  @override
+  String get rubyHintPinyin => 'With tone marks, e.g. hànzì';
+
   @override
   String get rubySave => 'Save';