feat(ui): PowerUse-Einstellungen nach Settings -> Ausfuehrung verschieben

Schalter, Zeitfenster und Handoff-Prozent lagen im Usage-Monitor und mussten
in SettingsModalViewModel nur load->save durchgeschleift werden, damit ein
Settings-Speichern sie nicht zurueckwirft. Jetzt gehoeren sie dem General-Tab,
der Monitor ist wieder nur Anzeige + Threshold-Drag, und "Jetzt aktualisieren"
sitzt als Icon in der Titelleiste (neuer ModalShell.HeaderActions-Slot).

docs/explore-notes/conpty-sessions.md

@@ -121,7 +121,7 @@ per call and `Register` clamps to min 1, so 0 can never mean "unbounded"). Past
 `wait`/`merge` request is silently coerced to its `_final` counterpart — check the result's
 `coerced` flag — and any handoff after a `merge_final` round throws.
 
-**PowerUse.** When `AppSettingsEntity.PowerUseEnabled` (toggled on the usage monitor) **and** the
+**PowerUse.** When `AppSettingsEntity.PowerUseEnabled` (Settings → Execution) **and** the
 list's own `ListConfigEntity.PowerUseAllowed` are both set, `InteractiveLaunchSpecService.
 ComposeHandlerPromptAsync` appends `PromptKind.PowerUseAddendum` to whichever handler prompt the
 phase resolved to. The addendum is written as an *override* of the base prompt's interactive rules

docs/explore-notes/usage-monitoring.md

@@ -254,6 +254,7 @@ degrades instead of throwing. Worker config: `usage_poll_interval_active_seconds
 `usage_poll_interval_idle_seconds`.
 
 The gate percentages are editable in **two** places that both write the same `app_settings` row:
-Settings → General (typed) and the usage-monitor gauges (dragged). The throttle stages are
+Settings → Execution (typed) and the usage-monitor gauges (dragged). The throttle stages are
 gauge-only — `SettingsModalViewModel` therefore carries them load→save verbatim so saving Settings
-can't reset a dragged value.
+can't reset a dragged value. PowerUse (switch, time window, handoff %) used to be usage-monitor-only
+and is now typed on the same Settings tab, so it needs no such round-trip.