Add cookie_policy_url field to cookie banners

Introduce a required cookie_policy_url alongside the existing
privacy_policy_url (now optional) so banners can link directly to a
dedicated cookie policy — a compliance best practice recommended by
CNIL, ICO, and the EDPB. Existing rows are seeded from their current
privacy_policy_url value.

Both {{cookie_policy_link}} and {{privacy_policy_link}} placeholders
are supported independently in banner description translations.

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

pkg/coredata/migrations/20260424T140000Z.sql

@@ -0,0 +1,8 @@
+-- Add cookie_policy_url (required) and make privacy_policy_url optional.
+-- Seed cookie_policy_url from existing privacy_policy_url for data continuity.
+
+ALTER TABLE cookie_banners ADD COLUMN cookie_policy_url TEXT NOT NULL DEFAULT '';
+
+UPDATE cookie_banners SET cookie_policy_url = privacy_policy_url WHERE cookie_policy_url = '';
+
+ALTER TABLE cookie_banners ALTER COLUMN privacy_policy_url DROP NOT NULL;