feat: add environment filtering across all APIs and UI

Backend: Added optional `environment` query parameter to catalog,
search, stats, timeseries, punchcard, top-errors, logs, and agents
endpoints. ClickHouse queries filter by environment when specified
(literal SQL for AggregatingMergeTree, ? binds for raw tables).
StatsStore interface methods all accept environment parameter.

UI: Added EnvironmentSelector component (compact native select).
LayoutShell extracts distinct environments from agent data and
passes selected environment to catalog and agent queries via URL
search param (?env=). TopBar shows current environment label.

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

ui/src/api/queries/catalog.ts

@@ -3,15 +3,16 @@ import { config } from '../../config';
 import { useAuthStore } from '../../auth/auth-store';
 import { useRefreshInterval } from './use-refresh-interval';
 
-export function useRouteCatalog(from?: string, to?: string) {
+export function useRouteCatalog(from?: string, to?: string, environment?: string) {
   const refetchInterval = useRefreshInterval(15_000);
   return useQuery({
-    queryKey: ['routes', 'catalog', from, to],
+    queryKey: ['routes', 'catalog', from, to, environment],
     queryFn: async () => {
       const token = useAuthStore.getState().accessToken;
       const params = new URLSearchParams();
       if (from) params.set('from', from);
       if (to) params.set('to', to);
+      if (environment) params.set('environment', environment);
       const qs = params.toString();
       const res = await fetch(`${config.apiBaseUrl}/routes/catalog${qs ? `?${qs}` : ''}`, {
         headers: {