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/Dashboard/Dashboard.tsx

@@ -12,6 +12,7 @@ import type { Column } from '@cameleer/design-system'
 import {
   useSearchExecutions,
 } from '../../api/queries/executions'
+import { useEnvironmentStore } from '../../api/environment-store'
 import type { ExecutionSummary } from '../../api/types'
 import { attributeBadgeColor } from '../../utils/attribute-color'
 import { formatDuration, statusLabel } from '../../utils/format-utils'
@@ -172,6 +173,7 @@ export default function Dashboard({ onExchangeSelect, activeExchangeId }: Dashbo
     if (activeExchangeId !== undefined) setSelectedId(activeExchangeId);
   }, [activeExchangeId]);
 
+  const selectedEnv = useEnvironmentStore((s) => s.environment);
   const { timeRange, statusFilters } = useGlobalFilters()
   const timeFrom = timeRange.start.toISOString()
   const timeTo = timeRange.end.toISOString()
@@ -192,6 +194,7 @@ export default function Dashboard({ onExchangeSelect, activeExchangeId }: Dashbo
       timeTo,
       routeId: routeId || undefined,
       applicationId: appId || undefined,
+      environment: selectedEnv,
       status: statusParam,
       text: textFilter,
       sortField,