Enforce Relay module-name prefix in naming

Relay 21 made the filename-prefix requirement opt-in for non-Haste
projects, and the relay/graphql-naming lint rule only covers
operations and legacy fragment containers, leaving hooks-based
fragment names unguarded. Re-enable compiler enforcement via
enforce_module_name_prefix_for_non_haste so fragments keep the
collision-free, navigable <ModuleName>_<localName> convention, and
document the rationale in the Relay guide. The compiler accepts the
current sources unchanged, so existing names already comply.

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

relay.config.json

@@ -1,7 +1,8 @@
 {
   "root": ".",
   "featureFlags": {
-    "enforce_fragment_alias_where_ambiguous": { "kind": "disabled" }
+    "enforce_fragment_alias_where_ambiguous": { "kind": "disabled" },
+    "enforce_module_name_prefix_for_non_haste": true
   },
   "sources": {
     "apps/console/src/pages/iam": "iam",