fix: auto-compute environment slug + respect environment filter globally

Part A: Environment creation slug is now auto-derived from display name
and shown read-only (matching app creation pattern). Removes manual slug
input.

Part B: All data queries now pass the selected environment to backend:
- Exchanges search, Dashboard L1/L2/L3 stats, Routes metrics, Route
  detail, correlation chains, and processor metrics all filter by
  selected environment.
- Backend RouteMetricsController now accepts environment parameter for
  both route and processor metrics endpoints.

Closes #XYZ

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ui/src/pages/DashboardTab/DashboardL3.tsx

@@ -14,6 +14,7 @@ import { useGlobalFilters } from '@cameleer/design-system';
 import { useExecutionStats, useStatsTimeseries } from '../../api/queries/executions';
 import { useProcessorMetrics } from '../../api/queries/processor-metrics';
 import { useTopErrors, useAppSettings } from '../../api/queries/dashboard';
+import { useEnvironmentStore } from '../../api/environment-store';
 import type { TopError } from '../../api/queries/dashboard';
 import { useDiagramByRoute } from '../../api/queries/diagrams';
 import { ProcessDiagram } from '../../components/ProcessDiagram';
@@ -244,16 +245,17 @@ function buildKpiItems(
 
 export default function DashboardL3() {
   const { appId, routeId } = useParams<{ appId: string; routeId: string }>();
+  const selectedEnv = useEnvironmentStore((s) => s.environment);
   const { timeRange } = useGlobalFilters();
   const timeFrom = timeRange.start.toISOString();
   const timeTo = timeRange.end.toISOString();
   const windowSeconds = (timeRange.end.getTime() - timeRange.start.getTime()) / 1000;
 
   // ── Data hooks ──────────────────────────────────────────────────────────
-  const { data: stats } = useExecutionStats(timeFrom, timeTo, routeId, appId);
-  const { data: timeseries } = useStatsTimeseries(timeFrom, timeTo, routeId, appId);
-  const { data: processorMetrics } = useProcessorMetrics(routeId ?? null, appId);
-  const { data: topErrors } = useTopErrors(timeFrom, timeTo, appId, routeId);
+  const { data: stats } = useExecutionStats(timeFrom, timeTo, routeId, appId, selectedEnv);
+  const { data: timeseries } = useStatsTimeseries(timeFrom, timeTo, routeId, appId, selectedEnv);
+  const { data: processorMetrics } = useProcessorMetrics(routeId ?? null, appId, selectedEnv);
+  const { data: topErrors } = useTopErrors(timeFrom, timeTo, appId, routeId, selectedEnv);
   const { data: diagramLayout } = useDiagramByRoute(appId, routeId);
   const { data: appSettings } = useAppSettings(appId);