Promote useMutation to the @probo/relay package

Extract the awaitable useMutation into @probo/relay as a
createUseMutation factory that delegates feedback to an injected
MutationNotifier, keeping the package free of UI and i18n
dependencies. compliance-portal binds it to its Base UI toast +
i18next + formatError stack and imports it by explicit path
(#/lib/relay/useMutation), dropping the lone intra-app barrel; a
compliance-portal-scoped no-restricted-imports rule forbids
react-relay's useMutation.

Bring packages/relay and packages/routes into the shared ESLint
scope and fix the violations that surfaced, and deprecate the
legacy withQueryRef / loaderFromQueryLoader helpers. Document the
shared-hook pattern and the "index.ts for package entrypoints only"
rule in the relay, hooks, and app-arborescence guides.

Signed-off-by: Émile Ré <emile@probo.com>

apps/compliance-portal/package.json

@@ -10,12 +10,16 @@
     "preview": "vite preview"
   },
   "dependencies": {
+    "@base-ui/react": "^1.6.0",
+    "@probo/helpers": "1.0.0",
     "@probo/react-lazy": "1.0.0",
+    "@probo/relay": "1.0.0",
     "@probo/routes": "1.0.0",
     "@probo/ui": "1.0.0",
-    "clsx": "^2.1.1",
+    "i18next": "^26.3.1",
     "react": "^19.2.7",
     "react-dom": "^19.2.7",
+    "react-i18next": "^17.0.8",
     "react-relay": "^21.0.1",
     "react-router": "^8.0.0",
     "relay-runtime": "^21.0.1"