Kosten je Einheit aufrechnen und Abweichungen melden (#699)

- IUsageRepository.GetDailyByAgentAsync: Tagessummen je Agent, Abo-Tokens getrennt
- UnitCosts: je Einheit samt Untereinheiten heute/7/30 Tage, Monat, Vormonat,
  Durchschnittstag (28 Tage, ab 7 Tagen Verlauf), Maximum = Summe der Agentengrenzen
- Meldungen: Abweichung vom eigenen Verlauf, Naehe zur Grenzsumme, Monatsschwellen
  der Instanz; CostWatch alle 15 min, je Einheit/Tag einmal (Tabelle CostAlerts),
  als Aufgabe an den Menschen; schaltet nichts ab
- API /usage/units, /usage/cost-alerts; Zeitreihe gruppiert nach Einheit
- WebUI: Karte "Kosten je Einheit" mit Meldungen in der Verbrauchsansicht; i18n en/de
- Einstellungen instance.json costWatch
- Tests: UnitCostsTests (8)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/ClawdDotNet.Manager.Web/wwwroot/i18n/en.json

@@ -671,6 +671,22 @@
   "usage.cost": "Cost",
   "usage.unknownPrice": "(price unknown)",
   "usage.notAvailable": "Usage data not available",
+  "usage.units.title": "Costs by unit",
+  "usage.units.hint": "Each unit with everything below it. The maximum is the sum of its agents' daily limits — limits stay at the agents. What matters is the change: a day far above the unit's own average is marked even when nothing is exceeded.",
+  "usage.units.unit": "Unit",
+  "usage.units.today": "Today",
+  "usage.units.average": "Average day",
+  "usage.units.max": "Max per day",
+  "usage.units.last7": "7 days",
+  "usage.units.thisMonth": "This month",
+  "usage.units.previousMonth": "Last month",
+  "usage.units.quota": "Quota (30 d)",
+  "usage.units.instance": "Instance",
+  "usage.units.topLevel": "Top level",
+  "usage.units.alerts": "Alerts of the last 7 days",
+  "usage.units.kind.Deviation": "Unusual day",
+  "usage.units.kind.NearLimit": "Near the limits",
+  "usage.units.kind.MonthlyThreshold": "Monthly total crossed",
   "usage.forecastTitle": "Cost Forecast",
   "usage.forecastDay": "Forecast per day",
   "usage.forecastMonth": "Forecast per month (30 days)",
@@ -783,6 +799,7 @@
   "timeline.metric.runs": "Runs",
   "timeline.groupBy": "By",
   "timeline.groupBy.agent": "Agent",
+  "timeline.groupBy.unit": "Unit",
   "timeline.groupBy.model": "Model",
   "timeline.groupBy.source": "Event",
   "timeline.groupBy.budget": "Budget",