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.Data/Models/AppSettingsEntity.cs

@@ -69,6 +69,17 @@ public sealed class AppSettingsEntity
     // run unattended. Composition lives in InteractiveLaunchSpecService.
     public bool PowerUseEnabled { get; set; }
 
+    // Optional local-time window (both `HH:mm`) narrowing when PowerUse applies, checked per phase
+    // at prompt-build time. Both null (the default) = round the clock, byte-identical to the
+    // pre-window behaviour; only one set counts as unset too. End before start wraps over midnight.
+    // Semantics live in PowerUseWindow.
+    public string? PowerUseWindowStart { get; set; }
+    public string? PowerUseWindowEnd { get; set; }
+
+    // Percentage of the 5h usage window at which a PowerUse handler session is told to hand off
+    // rather than start more work. Stored and displayed here; the consumer is the handoff prompt.
+    public int PowerUseHandoffPct { get; set; } = 95;
+
     // Server-side cap on a list-handler run's wait<->merge handoff chain (HandoffRoundTracker).
     // 4 = two full wait/merge cycles, the long-standing default. Raise it for a run meant to keep
     // going for hours. It exists to bound runaway handoff loops, so it must stay >= 1.

src/ClaudeDo.Data/Models/PowerUseWindow.cs

@@ -0,0 +1,32 @@
+namespace ClaudeDo.Data.Models;
+
+/// <summary>
+/// The optional local-time window restricting when PowerUse applies
+/// (<see cref="AppSettingsEntity.PowerUseWindowStart"/> / <c>End</c>, both <c>HH:mm</c>).
+/// Pure on purpose — the caller supplies "now", so the window logic is testable without a clock.
+/// </summary>
+public static class PowerUseWindow
+{
+    /// <summary>Parses an <c>HH:mm</c> string; anything else (including null/blank) is null.</summary>
+    public static TimeOnly? Parse(string? value)
+        => TimeOnly.TryParseExact(value?.Trim(), "HH:mm", out var t) ? t : null;
+
+    /// <summary>Round-trips a stored/typed value through <see cref="Parse"/>, so an unparseable
+    /// string is stored as null instead of sitting in the column pretending to be a window.</summary>
+    public static string? Normalize(string? value) => Parse(value)?.ToString("HH:mm");
+
+    /// <summary>
+    /// True when <paramref name="now"/> falls inside the window. Half-open: start is included,
+    /// end is not. Either bound missing = no window at all = always true (the pre-window
+    /// behaviour). A window whose end is before its start wraps over midnight.
+    /// </summary>
+    public static bool Contains(TimeOnly now, TimeOnly? start, TimeOnly? end)
+    {
+        if (start is not { } from || end is not { } to) return true;
+        return from < to ? now >= from && now < to : now >= from || now < to;
+    }
+
+    /// <summary>Convenience overload for the two stored strings and a wall clock.</summary>
+    public static bool IsOpen(DateTime now, string? start, string? end)
+        => Contains(TimeOnly.FromDateTime(now), Parse(start), Parse(end));
+}