refactor: rename @crema/arcadia-client → @crema/arcadia-core-client

Disambiguates the Phoenix/auth client lib from lib-arcadia-agents-client.
Dir lib-arcadia-client → lib-arcadia-core-client; alias updated in
tsconfig paths, vite config, app.css @source, imports, CI and docs.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

package.json

@@ -9,6 +9,6 @@
     ".": "./src/index.tsx"
   },
   "peerDependencies": {
-    "@crema/arcadia-client": "*"
+    "@crema/arcadia-core-client": "*"
   }
 }