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/coredata/migrations/20260721T084500Z.sql

@@ -0,0 +1,2 @@
+ALTER TABLE identities
+ADD COLUMN locale TEXT NULL;