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.Web/Endpoints/AnalyticsEndpoints.cs

@@ -58,9 +58,39 @@ public static class AnalyticsEndpoints
                 groupBy is "model" or "source" or "budget" ? groupBy : "agent",
                 TimeSpan.FromMinutes(Math.Clamp(tzOffset, -14 * 60, 14 * 60)),
                 ct);
+
+            // #699: "What does marketing cost me?" — the agents' series, added up by their unit as it is now.
+            if (groupBy == "unit")
+            {
+                var org = host.Organisation.Current();
+                return Results.Ok(points
+                    .GroupBy(p => (p.BucketStart, Unit: org.UnitOf(p.Group) is { } u ? org.PathOf(u.Id) : "—"))
+                    .Select(g => new SeriesPointDto(g.Key.BucketStart, g.Key.Unit, g.Sum(p => p.Runs), g.Sum(p => p.Tokens), g.Sum(p => p.CostUsd)))
+                    .OrderBy(p => p.BucketStart)
+                    .ToList());
+            }
             return Results.Ok(points.Select(p => new SeriesPointDto(p.BucketStart, p.Group, p.Runs, p.Tokens, p.CostUsd)).ToList());
         });
 
+        // #699: Costs per unit — itself and everything below it — with the alerts raised on them.
+        api.MapGet("/usage/units", async (AppHost host, CancellationToken ct) =>
+        {
+            if (host.CostWatch is not { } watch)
+                return ApiEndpoints.Unavailable("No usage data: agents are not active.");
+            var lines = await watch.ReportAsync(ct);
+            return Results.Ok(lines.Select(l => new UnitCostDto(
+                l.UnitId, l.Name, l.Path, l.Depth, l.Agents, l.Today, l.Last7Days, l.Last30Days, l.ThisMonth, l.PreviousMonth,
+                l.MaxPerDay, l.AverageDay, l.ShareOfMaxToday, l.SubscriptionTokensToday, l.SubscriptionTokens30Days)).ToList());
+        });
+
+        api.MapGet("/usage/cost-alerts", async (AppHost host, CancellationToken ct, int days = 30) =>
+        {
+            if (host.CostWatch is not { } watch)
+                return Results.Ok(Array.Empty<CostAlertDto>());
+            return Results.Ok((await watch.RecentAsync(days, ct))
+                .Select(a => new CostAlertDto(a.Period, a.Scope, a.Kind.ToString(), a.Message, a.RaisedAt)).ToList());
+        });
+
         api.MapGet("/usage/events", async (AppHost host, HttpRequest request, CancellationToken ct) =>
         {
             if (host.Insights is not { } insights)