Fix the language picker and tidy the graphics tab

Both language combos decided a change was the user's by checking
IsKeyboardFocusWithin on the picked item. Selecting with the mouse leaves the
focus on the combo, not on the item, so on Windows the check failed and the
language never changed. The handlers now compare the picked code with the one
already loaded instead of guessing who caused the event: filling the combo in
selects what is loaded and stops there, a real pick differs and applies.

The settings tab listed a hard-coded Polski / English pair and wrote the
language back as "Polski" or "English", so picking Czech, Hungarian or
Russian in the top bar was overwritten on save. It is filled from lang/ now,
and writes back the selected entry.

LocalizationService gains a LanguageChanged event: the main window rebuilds
the captions that code builds once (train stats, panel headers, combo items)
from there, so a pick in either place refreshes them. Its PropertyChanged
also names the indexer "Item[]", which is what bindings listen for.

Graphics tab: the track-curve quality slider moves over from Physics, the
view angle shows a degree sign instead of the Polish "stopni", and the HDR
tone-mapping picker is gone - only Reinhard.glsl ever shipped, so
ApplyHdrShader copies that one and the starter.hdr setting is dropped.

StarterNG/Services/LocalizationService.cs

@@ -29,6 +29,13 @@ public class LocalizationService : INotifyPropertyChanged
 
     public event PropertyChangedEventHandler? PropertyChanged;
 
+    /// <summary>
+    /// Raised after a language file is loaded. XAML bindings refresh themselves
+    /// through <see cref="PropertyChanged"/>; this is for captions that code
+    /// builds once and has to build again.
+    /// </summary>
+    public event Action? LanguageChanged;
+
     /// <summary>Display name of the active language (e.g. "English", "Polski").</summary>
     public string CurrentLanguage { get; private set; } = "English";
 
@@ -113,7 +120,11 @@ public class LocalizationService : INotifyPropertyChanged
             CurrentLanguage = "English";
         }
 
-        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs("Item"));
+        // "Item[]" is the indexer name bindings listen for; the empty name asks
+        // every binding on this object to re-read.
+        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs("Item[]"));
+        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(string.Empty));
+        LanguageChanged?.Invoke();
         return CurrentLanguage;
     }