feat(ui): PowerUse-Toggle im Usage-Monitor, Opt-in pro Liste

Der Toggle sitzt unter den Gauges im Usage-Monitor, weil "das restliche Fenster
ausnutzen" eine Entscheidung ist, die man beim Blick auf das restliche Fenster
trifft. Er speichert sofort per Read-modify-write, gleiche Disziplin wie
SaveStagesAsync, damit er keine Felder ueberschreibt, die er nicht besitzt.

Zwei Stellen, die das Opt-in still ausgeschaltet haetten:
- WorkerHub.UpdateListConfig loescht die Config-Zeile, wenn alle Felder leer
  sind. PowerUseAllowed muss in diese Leer-Pruefung, sonst verschwindet das
  Opt-in sofort wieder, wenn es das einzige gesetzte Feld ist.
- SettingsModalViewModel baut das AppSettingsDto positional neu auf. Ohne
  Round-trip haette jedes Speichern der Settings PowerUseEnabled auf den
  Record-Default false zurueckgesetzt. Gleiches Muster wie _throttleStages.

Das Handoff-Budget ist als Spinner in Settings -> General editierbar, weil es
auch fuer normale (interaktive) Handler-Runs gilt und nicht an PowerUse haengt.
Das Addendum selbst ist ueber Settings -> Files anpassbar.

src/ClaudeDo.Localization/locales/en.json

@@ -41,6 +41,8 @@
       "usageGateSevenDayPct": "7-day window (%)",
       "autoContinueOnUsageLimit": "Continue on session limit reset",
       "autoContinueOnUsageLimitHint": "When a run stops because it hit the usage limit, automatically continue it once the 5-hour window resets. Also wakes the paused queue exactly at reset time instead of waiting for the next backstop check.",
+      "listHandlerMaxHandoffs": "List-handler handoff budget",
+      "listHandlerMaxHandoffsHint": "How many wait/merge handoffs one \"Let Claude handle it\" run may chain. 4 means two merge rounds. Raise it for runs meant to keep going for hours; it bounds a runaway chain, so it cannot be 0.",
       "throttleStagesHeading": "Throttle stages",
       "throttleStagesHint": "Parallelism is capped before the hard gate: soft caps at 2 slots, hard at 1. Edited by dragging the markers on the usage-monitor gauges. Opening the monitor closes these settings — save first if you changed anything.",
       "throttleStagesValues": "5h: soft {0}% / hard {1}%  ·  7d: soft {2}% / hard {3}%",
@@ -85,6 +87,7 @@
       "retryPrompt": "Retry",
       "dailyPrepPrompt": "Daily prep",
       "weeklyReportPrompt": "Weekly report",
+      "powerUsePrompt": "PowerUse addendum",
       "viewPrompt": "View",
       "customizedSection": "CUSTOMIZED",
       "customizedHint": "These prompts differ from the bundled default and are kept as-is. Reset to pick up future default improvements.",
@@ -398,6 +401,8 @@
       "manualListHint": "New tasks in this list start out manual: no queueing, running or refining, and automation skips them. You can still open a hand-driven session.",
       "findingsTracked": "Commit the .claudedo findings folder",
       "findingsTrackedHint": "Off: the folder stays out of git via .git/info/exclude. On: findings travel with the repo.",
+      "powerUseAllowed": "Allow PowerUse for this list",
+      "powerUseAllowedHint": "Lets a list-handler run on this list go unattended when PowerUse is switched on in the usage monitor: it asks nothing, resolves conflicts itself, and harvests new work. Both switches are needed, so leaving PowerUse on globally never changes a list that hasn't opted in.",
       "sectionIcon": "ICON",
       "icon": "List icon",
       "iconHint": "Shown next to the list name in the sidebar.",
@@ -504,6 +509,8 @@
       "title": "USAGE MONITOR",
       "windowTitle": "Usage Monitor",
       "noGauges": "No usage limits reported yet.",
+      "powerUse": "PowerUse",
+      "powerUseHint": "Spend the rest of the window: a list-handler run asks nothing, resolves conflicts itself, harvests new work, and keeps handing off for as long as its budget allows. Only affects lists that allowed PowerUse in their list settings.",
       "refresh": "Refresh now",
       "refreshHint": "Polled every 5 min while a task runs, otherwise every 15 min.",
       "staleFormat": "Values stale (as of {0})",
@@ -749,6 +756,7 @@
       "loadFailed": "Couldn't load usage data: {0}",
       "refreshFailed": "Couldn't refresh usage: {0}",
       "thresholdSaveFailed": "Couldn't save the threshold: {0}",
+      "powerUseSaveFailed": "Couldn't save the PowerUse switch: {0}",
       "installStarted": "Installing TokenTracker — watch the log strip for progress.",
       "installFailed": "Couldn't install TokenTracker: {0}",
       "analyticsRefreshFailed": "Couldn't refresh the analytics: {0}",