feat(usage): PowerUse-Zeitfenster + Handoff-Schwellwert als Settings

Drei neue app_settings-Spalten (Migration AddPowerUseWindow):
power_use_window_start/end (HH:mm, lokal, nullable) und
power_use_handoff_pct (NOT NULL DEFAULT 95, geclampt 50-99).

Die Fensterlogik liegt als reine Funktion in PowerUseWindow
(Contains/Normalize/IsOpen): beide Grenzen leer oder nur eine gesetzt =
rund um die Uhr, Ende vor Start wrappt ueber Mitternacht, Grenzen
halboffen. Geprueft wird in ComposeHandlerPromptAsync, also pro Phase
zum Zeitpunkt des Prompt-Baus - die Uhr ist per Func<DateTime>
injizierbar. Bedienung im Usage-Monitor neben dem PowerUse-Toggle
(Commit auf Blur/Enter, ein Write fuer alle vier Felder); in
Settings->General unsichtbar, aber load->save durchgereicht.

Nebenbefund, gleicher Pfad: AppSettingsRepository.UpdateAsync kopiert
Feld fuer Feld und hat ModelPresets, PowerUseEnabled und
ListHandlerMaxHandoffs nie geschrieben - jeder Save dieser drei war
still wirkungslos. Mit ergaenzt und per Round-trip-Test gepinnt.

src/ClaudeDo.Ui/ViewModels/Modals/SettingsModalViewModel.cs

@@ -134,6 +134,10 @@ public sealed partial class SettingsModalViewModel : ViewModelBase
     // opening and saving Settings can't switch it off behind the user's back.
     private bool _powerUseEnabled;
 
+    // Ditto for the PowerUse time window and handoff threshold — usage-monitor-owned, invisible
+    // here, but they must survive a Settings save.
+    private (string? Start, string? End, int HandoffPct) _powerUseWindow = (null, null, 95);
+
     public async Task LoadAsync()
     {
         IsBusy = true;
@@ -156,6 +160,7 @@ public sealed partial class SettingsModalViewModel : ViewModelBase
                 // because SaveAsync rebuilds the whole DTO positionally and would otherwise write
                 // the record default (false) back and silently switch PowerUse off.
                 _powerUseEnabled = dto.PowerUseEnabled;
+                _powerUseWindow = (dto.PowerUseWindowStart, dto.PowerUseWindowEnd, dto.PowerUseHandoffPct);
                 _throttleStages = (
                     dto.UsageThrottleFiveHourSoftPct, dto.UsageThrottleFiveHourHardPct,
                     dto.UsageThrottleSevenDaySoftPct, dto.UsageThrottleSevenDayHardPct);
@@ -224,7 +229,10 @@ public sealed partial class SettingsModalViewModel : ViewModelBase
                 _throttleStages.SevenHard,
                 General.AutoContinueOnUsageLimit,
                 _powerUseEnabled,
-                General.ListHandlerMaxHandoffs);
+                General.ListHandlerMaxHandoffs,
+                _powerUseWindow.Start,
+                _powerUseWindow.End,
+                _powerUseWindow.HandoffPct);
             await _worker.UpdateAppSettingsAsync(dto);
             await Prime.SaveAsync();
             await OnlineInbox.SaveAsync();

src/ClaudeDo.Ui/ViewModels/Modals/UsageMonitorModalViewModel.cs

@@ -2,6 +2,7 @@ using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Threading.Tasks;
+using ClaudeDo.Data.Models;
 using ClaudeDo.Ui.Localization;
 using ClaudeDo.Ui.Services;
 using CommunityToolkit.Mvvm.ComponentModel;
@@ -108,6 +109,14 @@ public sealed partial class UsageMonitorModalViewModel : ViewModelBase
     /// </summary>
     [ObservableProperty] private bool _powerUseEnabled;
 
+    /// <summary>Optional local-time window (<c>HH:mm</c>) narrowing when PowerUse applies. Both
+    /// blank = round the clock. Committed on focus loss / Enter, not per keystroke.</summary>
+    [ObservableProperty] private string? _powerUseWindowStart;
+    [ObservableProperty] private string? _powerUseWindowEnd;
+
+    /// <summary>5h-usage percentage at which a PowerUse handler session should hand off.</summary>
+    [ObservableProperty] private int _powerUseHandoffPct = 95;
+
     // Set while LoadAsync writes the stored value in, so seeding the property doesn't immediately
     // write it straight back to the worker.
     private bool _loadingPowerUse;
@@ -115,13 +124,16 @@ public sealed partial class UsageMonitorModalViewModel : ViewModelBase
     partial void OnPowerUseEnabledChanged(bool value)
     {
         if (_loadingPowerUse) return;
-        _ = SavePowerUseAsync(value);
+        _ = SavePowerUse();
     }
 
     /// Read-modify-write, same discipline as SaveStagesAsync: never clobber a field this modal
-    /// doesn't own.
-    private async Task SavePowerUseAsync(bool value)
+    /// doesn't own. All four PowerUse fields go in one write, so committing one box can't drop a
+    /// value the user just typed into a sibling box.
+    [RelayCommand]
+    private async Task SavePowerUse()
     {
+        if (_loadingPowerUse) return;
         try
         {
             var settings = await _worker.GetAppSettingsAsync();
@@ -131,7 +143,28 @@ public sealed partial class UsageMonitorModalViewModel : ViewModelBase
                 return;
             }
 
-            await _worker.UpdateAppSettingsAsync(settings with { PowerUseEnabled = value });
+            // The worker stores an unparseable time as null; normalize here too so the box shows
+            // what was actually saved instead of a typo that looks like a live window.
+            var start = PowerUseWindow.Normalize(PowerUseWindowStart);
+            var end = PowerUseWindow.Normalize(PowerUseWindowEnd);
+            var pct = Math.Clamp(PowerUseHandoffPct, 50, 99);
+
+            await _worker.UpdateAppSettingsAsync(settings with
+            {
+                PowerUseEnabled = PowerUseEnabled,
+                PowerUseWindowStart = start,
+                PowerUseWindowEnd = end,
+                PowerUseHandoffPct = pct,
+            });
+
+            _loadingPowerUse = true;
+            try
+            {
+                PowerUseWindowStart = start;
+                PowerUseWindowEnd = end;
+                PowerUseHandoffPct = pct;
+            }
+            finally { _loadingPowerUse = false; }
         }
         catch (Exception ex)
         {
@@ -192,7 +225,13 @@ public sealed partial class UsageMonitorModalViewModel : ViewModelBase
             if (settings is not null)
             {
                 _loadingPowerUse = true;
-                try { PowerUseEnabled = settings.PowerUseEnabled; }
+                try
+                {
+                    PowerUseEnabled = settings.PowerUseEnabled;
+                    PowerUseWindowStart = settings.PowerUseWindowStart;
+                    PowerUseWindowEnd = settings.PowerUseWindowEnd;
+                    PowerUseHandoffPct = settings.PowerUseHandoffPct;
+                }
                 finally { _loadingPowerUse = false; }
             }