feat: add account settings page with theme choice

src/FamilyPlanner.Web.Client/Layout/UserMenu.razor

@@ -16,6 +16,9 @@
                     <MudText Typo="Typo.caption">@string.Join(", ", RolesOf(auth.User))</MudText>
                 </div>
                 <MudDivider />
+                <MudMenuItem Icon="@Icons.Material.Filled.Settings" OnClick="@(() => Navigation.NavigateTo("konto/einstellungen"))">
+                    Meine Einstellungen
+                </MudMenuItem>
                 <MudMenuItem Icon="@Icons.Material.Filled.Password" OnClick="@(() => Navigation.NavigateTo("konto/passwort"))">
                     Passwort ändern
                 </MudMenuItem>

src/FamilyPlanner.Web.Client/Pages/AccountSettings.razor

@@ -0,0 +1,26 @@
+@page "/konto/einstellungen"
+@inject ThemeState Theme
+
+<PageTitle>Meine Einstellungen – Familienplaner</PageTitle>
+
+<MudText Typo="Typo.h4" HtmlTag="h1" Class="mb-4">Meine Einstellungen</MudText>
+
+<MudPaper Outlined="true" Class="pa-4 fp-account-settings" Style="max-width: 640px">
+    <MudText Typo="Typo.h6" HtmlTag="h2" Class="mb-2">Darstellung</MudText>
+    <MudRadioGroup T="ThemePreference" Value="Theme.Preference" ValueChanged="OnThemeChangedAsync" Class="fp-theme-choice">
+        <MudRadio T="ThemePreference" Value="ThemePreference.System" Color="Color.Primary">Wie das Gerät</MudRadio>
+        <MudRadio T="ThemePreference" Value="ThemePreference.Light" Color="Color.Primary">Hell</MudRadio>
+        <MudRadio T="ThemePreference" Value="ThemePreference.Dark" Color="Color.Primary">Dunkel</MudRadio>
+    </MudRadioGroup>
+
+    <MudDivider Class="my-4" />
+
+    <MudText Typo="Typo.h6" HtmlTag="h2" Class="mb-2">Benachrichtigungen</MudText>
+    <MudText Typo="Typo.body2" Class="mb-2">Erinnerungen auf diesem Gerät ein- oder ausschalten.</MudText>
+    <MudButton Href="konto/benachrichtigungen" Variant="Variant.Outlined" Color="Color.Primary" Class="fp-settings-notifications"
+               StartIcon="@Icons.Material.Filled.Notifications">Benachrichtigungen einstellen</MudButton>
+</MudPaper>
+
+@code {
+    private Task OnThemeChangedAsync(ThemePreference preference) => Theme.SetPreferenceAsync(preference);
+}

src/FamilyPlanner.Web.Client/Services/ThemeState.cs

@@ -45,4 +45,12 @@ public sealed class ThemeState(IJSRuntime js)
         await js.InvokeVoidAsync("familyPlanner.theme.save", Preference.ToString());
         Changed?.Invoke();
     }
+
+    /// <summary>Setzt die Wahl ausdrücklich (System/Hell/Dunkel) und speichert sie lokal.</summary>
+    public async Task SetPreferenceAsync(ThemePreference preference)
+    {
+        Preference = preference;
+        await js.InvokeVoidAsync("familyPlanner.theme.save", Preference.ToString());
+        Changed?.Invoke();
+    }
 }