feat!: environment admin URLs use slug; validate and immutabilize slug

UUID-based admin paths were the only remaining UUID-in-URL pattern in
the API. Migrates /api/v1/admin/environments/{id} to /{envSlug} so
slugs are the single environment identifier in every URL. UUIDs stay
internal to the database.

- Controller: @PathVariable UUID id → @PathVariable String envSlug on
  get/update/delete and the two nested endpoints (default-container-
  config, jar-retention). Handlers resolve slug → Environment via
  EnvironmentService.getBySlug, then delegate to existing UUID-based
  service methods.
- Service: create() now validates slug against ^[a-z0-9][a-z0-9-]{0,63}$
  and returns 400 on invalid slugs. Rationale documented in the class:
  slugs are immutable after creation because they appear in URLs,
  Docker network names, container names, and ClickHouse partition keys.
- UpdateEnvironmentRequest has no slug field and Jackson's default
  ignore-unknown behavior drops any slug supplied in a PUT body;
  regression test (updateEnvironment_withSlugInBody_ignoresSlug)
  documents this invariant.
- SPA: mutation args change from { id } to { slug }. EnvironmentsPage
  still uses env.id for local selection state (UUID from DB) but
  passes env.slug to every mutation.

BREAKING CHANGE: /api/v1/admin/environments/{id:UUID}/... paths removed.
Clients must use /{envSlug}/... (slug from the environments list).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

ui/src/api/queries/admin/environments.ts

@@ -46,8 +46,8 @@ export function useCreateEnvironment() {
 export function useUpdateEnvironment() {
   const qc = useQueryClient();
   return useMutation({
-    mutationFn: ({ id, ...req }: UpdateEnvironmentRequest & { id: string }) =>
-      adminFetch<Environment>(`/environments/${id}`, {
+    mutationFn: ({ slug, ...req }: UpdateEnvironmentRequest & { slug: string }) =>
+      adminFetch<Environment>(`/environments/${slug}`, {
         method: 'PUT',
         body: JSON.stringify(req),
       }),
@@ -58,8 +58,8 @@ export function useUpdateEnvironment() {
 export function useUpdateDefaultContainerConfig() {
   const qc = useQueryClient();
   return useMutation({
-    mutationFn: ({ id, config }: { id: string; config: Record<string, unknown> }) =>
-      adminFetch<Environment>(`/environments/${id}/default-container-config`, {
+    mutationFn: ({ slug, config }: { slug: string; config: Record<string, unknown> }) =>
+      adminFetch<Environment>(`/environments/${slug}/default-container-config`, {
         method: 'PUT',
         body: JSON.stringify(config),
       }),
@@ -70,8 +70,8 @@ export function useUpdateDefaultContainerConfig() {
 export function useUpdateJarRetention() {
   const qc = useQueryClient();
   return useMutation({
-    mutationFn: ({ id, jarRetentionCount }: { id: string; jarRetentionCount: number | null }) =>
-      adminFetch<Environment>(`/environments/${id}/jar-retention`, {
+    mutationFn: ({ slug, jarRetentionCount }: { slug: string; jarRetentionCount: number | null }) =>
+      adminFetch<Environment>(`/environments/${slug}/jar-retention`, {
         method: 'PUT',
         body: JSON.stringify({ jarRetentionCount }),
       }),
@@ -82,8 +82,8 @@ export function useUpdateJarRetention() {
 export function useDeleteEnvironment() {
   const qc = useQueryClient();
   return useMutation({
-    mutationFn: (id: string) =>
-      adminFetch<void>(`/environments/${id}`, { method: 'DELETE' }),
+    mutationFn: (slug: string) =>
+      adminFetch<void>(`/environments/${slug}`, { method: 'DELETE' }),
     onSuccess: () => qc.invalidateQueries({ queryKey: ['admin', 'environments'] }),
   });
 }