feat(study): limits switch on and off, step by 5, and take any number typed

Your calls (2026-10-11): a switch per limit, and steps of 5 with any
number typed.

- A daily limit (new cards, reviews; in a studyset's study options and the
  study settings) is a switch, "Limit new cards per day", and its number
  while on. Counting down to 0 for no limit had to be guessed, and a goal
  has nothing like it. Switched off and on again, the limit comes back as
  it was; the first time, at the defaults' 20 new cards, or 200 reviews as
  Anki starts them. Stored as before: 0 still stands for none.
- The study goal counts in steps of 5 as the limits do (reviews: 25).
  Plus and minus go to the next multiple, so 12 steps to 15 or 10, never
  below the first step.
- Tapping the number lets any other be typed, from 1 (CountStepper.onTyped).

Pomodoro minutes and cards per round keep their own steps.

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

@@ -3231,6 +3231,15 @@ class AppLocalizationsDe extends AppLocalizations {
   @override
   String get studyMore => 'Erhöhen';
 
+  @override
+  String get countStepperType => 'Zahl eingeben';
+
+  @override
+  String get studyLimitNewPerDay => 'Neue Karten pro Tag begrenzen';
+
+  @override
+  String get studyLimitReviewsPerDay => 'Wiederholungen pro Tag begrenzen';
+
   @override
   String get studysetMenuReset => 'Fortschritt zurücksetzen';