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>

cameleer-server-core/src/main/java/com/cameleer/server/core/runtime/EnvironmentService.java

@@ -3,8 +3,19 @@ package com.cameleer.server.core.runtime;
 import java.util.List;
 import java.util.Map;
 import java.util.UUID;
+import java.util.regex.Pattern;
 
 public class EnvironmentService {
+
+    /**
+     * Slug must start with a lowercase letter or digit, contain only lowercase
+     * letters, digits, and hyphens, and be 1–64 characters long. Slugs are
+     * immutable after creation — they appear in URLs, Docker network names,
+     * container names, and ClickHouse partition keys, so renaming is not
+     * supported by design.
+     */
+    private static final Pattern SLUG_PATTERN = Pattern.compile("^[a-z0-9][a-z0-9-]{0,63}$");
+
     private final EnvironmentRepository repo;
 
     public EnvironmentService(EnvironmentRepository repo) {
@@ -22,6 +33,10 @@ public class EnvironmentService {
     }
 
     public UUID create(String slug, String displayName, boolean production) {
+        if (slug == null || !SLUG_PATTERN.matcher(slug).matches()) {
+            throw new IllegalArgumentException(
+                    "Invalid slug: must match ^[a-z0-9][a-z0-9-]{0,63}$ (lowercase letters, digits, hyphens)");
+        }
         if (repo.findBySlug(slug).isPresent()) {
             throw new IllegalArgumentException("Environment with slug '" + slug + "' already exists");
         }