feat(learn): spelling and grammar checked as people write (ADR 0024)

Where the instance's LanguageTool checks the language, the editors
underline what it finds after a pause, a paragraph at a time, a tap
offering its suggestions (GrammarHost, GrammarCheckController,
GrammarOverlay; nothing written into the document). A card's front is
checked in the studyset's front language, its back and answers in the
back's, everything else in the language recognised.

In a private studyset nothing is sent until the person agrees for it,
asked once in a banner above the editor and kept in their settings
(an agreement under privateAgreements, a refusal in grammarDeclined,
settings schema 14), taken back in the studyset's privacy dialog.
Settings > Writing turns it off on the device.

The field's Check asks LanguageTool first where it checks the
studyset's language, in a sheet offering to ask the assistant why;
elsewhere it asks the assistant as before (amends ADR 0021, D54).

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

apps/learn/halkyon_learn_flutter/lib/l10n/app_localizations.dart

@@ -3508,6 +3508,30 @@ abstract class AppLocalizations {
   /// **'Show the focus / break countdown inside the study session, so you can see the time left without opening the notification.'**
   String get settingsStudyPomodoroSubtitle;
 
+  /// Settings' card on checking what is written (ADR 0024).
+  ///
+  /// In en, this message translates to:
+  /// **'Writing'**
+  String get settingsWriting;
+
+  /// No description provided for @settingsGrammarTitle.
+  ///
+  /// In en, this message translates to:
+  /// **'Check grammar while writing'**
+  String get settingsGrammarTitle;
+
+  /// No description provided for @settingsGrammarSubtitle.
+  ///
+  /// In en, this message translates to:
+  /// **'Underline possible spelling and grammar mistakes in flashcards and notes, with one-tap fixes. Checks run when you pause, in the studyset\'s languages.'**
+  String get settingsGrammarSubtitle;
+
+  /// Below the switch where the instance runs no LanguageTool.
+  ///
+  /// In en, this message translates to:
+  /// **'This instance has no spelling and grammar check set up yet, so nothing is underlined. Left on, checking starts once it has one.'**
+  String get settingsGrammarUnavailable;
+
   /// No description provided for @settingsVersion.
   ///
   /// In en, this message translates to:
@@ -11102,6 +11126,24 @@ abstract class AppLocalizations {
   /// **'Take back'**
   String get studysetPrivacyTakeBack;
 
+  /// The privacy dialog's answer on checking what is written (ADR 0024).
+  ///
+  /// In en, this message translates to:
+  /// **'Spelling and grammar'**
+  String get studysetPrivacyGrammar;
+
+  /// No description provided for @studysetPrivacyGrammarChecked.
+  ///
+  /// In en, this message translates to:
+  /// **'Checked by {instance} as you write'**
+  String studysetPrivacyGrammarChecked(String instance);
+
+  /// No description provided for @studysetPrivacyGrammarNotChecked.
+  ///
+  /// In en, this message translates to:
+  /// **'Not checked as you write'**
+  String get studysetPrivacyGrammarNotChecked;
+
   /// After a card was rated Bad (ADR 0021, D53); name is the assistant's.
   ///
   /// In en, this message translates to:
@@ -11138,6 +11180,78 @@ abstract class AppLocalizations {
   /// **'Check for mistakes'**
   String get assistantCheck;
 
+  /// In place of suggestions for a mistake that has none.
+  ///
+  /// In en, this message translates to:
+  /// **'No suggestions'**
+  String get grammarNoSuggestions;
+
+  /// No description provided for @grammarNothingFound.
+  ///
+  /// In en, this message translates to:
+  /// **'No spelling or grammar mistakes found'**
+  String get grammarNothingFound;
+
+  /// The banner above an editor in a private studyset not asked yet (ADR 0024).
+  ///
+  /// In en, this message translates to:
+  /// **'Check spelling and grammar in this private studyset? While it is checked, what you write here goes to {instance} readable, a paragraph at a time; neither the instance nor its LanguageTool keeps any of it. You\'re asked once for this studyset and its topics.'**
+  String grammarPrivateAsk(String instance);
+
+  /// No description provided for @grammarPrivateNotHere.
+  ///
+  /// In en, this message translates to:
+  /// **'Not here'**
+  String get grammarPrivateNotHere;
+
+  /// No description provided for @grammarPrivateCheckHere.
+  ///
+  /// In en, this message translates to:
+  /// **'Check here'**
+  String get grammarPrivateCheckHere;
+
+  /// The field's Check sheet, what the instance's LanguageTool found.
+  ///
+  /// In en, this message translates to:
+  /// **'Spelling and grammar'**
+  String get grammarCheckTitle;
+
+  /// No description provided for @grammarCheckTooOften.
+  ///
+  /// In en, this message translates to:
+  /// **'Checked too often for now. Try again in a minute.'**
+  String get grammarCheckTooOften;
+
+  /// No description provided for @grammarCheckTooLong.
+  ///
+  /// In en, this message translates to:
+  /// **'Too long to check at once.'**
+  String get grammarCheckTooLong;
+
+  /// No description provided for @grammarCheckUnknownLanguage.
+  ///
+  /// In en, this message translates to:
+  /// **'The instance doesn\'t check this language.'**
+  String get grammarCheckUnknownLanguage;
+
+  /// No description provided for @grammarCheckFailed.
+  ///
+  /// In en, this message translates to:
+  /// **'The instance\'s check couldn\'t be reached. Try again later.'**
+  String get grammarCheckFailed;
+
+  /// No description provided for @grammarCheckAskWhy.
+  ///
+  /// In en, this message translates to:
+  /// **'Ask {name} why'**
+  String grammarCheckAskWhy(String name);
+
+  /// No description provided for @grammarCheckAskInstead.
+  ///
+  /// In en, this message translates to:
+  /// **'Ask {name} to check'**
+  String grammarCheckAskInstead(String name);
+
   /// The sheet of cards an assistant proposes (ADR 0021, D55).
   ///
   /// In en, this message translates to: