Put locale in compliance portal URLs

Path-segment locales make each language crawlable with self
canonical and hreflang, while identity.locale persists an
explicit choice without client storage or cookie banners.

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

pkg/server/api/complianceportal/v1/graphql/auth.graphql

@@ -1,6 +1,8 @@
 extend type Mutation {
   updateFullName(input: UpdateFullNameInput!): UpdateFullNamePayload
     @authentication(required: PRESENT) @sessionOnly
+  updateLocale(input: UpdateLocaleInput!): UpdateLocalePayload
+    @authentication(required: PRESENT) @sessionOnly
   signOut: SignOutPayload! @authentication(required: PRESENT) @sessionOnly
 }
 
@@ -12,6 +14,15 @@ type UpdateFullNamePayload {
   success: Boolean!
 }
 
+input UpdateLocaleInput {
+  # Short URL locale tag (en, fr, de, …).
+  locale: String!
+}
+
+type UpdateLocalePayload {
+  identity: Identity!
+}
+
 type SignOutPayload {
   success: Boolean!
 }