Add uncategorised cookie category

Replace the `required` boolean column on cookie_categories with a `kind`
enum (NORMAL, NECESSARY, UNCATEGORISED). The Necessary category remains
undeletable and always-on for consent; the new Uncategorised category is
also undeletable but users can opt out of it.

When a category is deleted, its cookies are merged into the Uncategorised
category (lazy-created for legacy banners that don't have one yet).

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

pkg/coredata/migrations/20260420T143027Z.sql

@@ -0,0 +1,27 @@
+-- Copyright (c) 2026 Probo Inc <hello@getprobo.com>.
+--
+-- Permission to use, copy, modify, and/or distribute this software for any
+-- purpose with or without fee is hereby granted, provided that the above
+-- copyright notice and this permission notice appear in all copies.
+--
+-- THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+-- REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+-- AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+-- INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+-- LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+-- OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+-- PERFORMANCE OF THIS SOFTWARE.
+
+CREATE TYPE cookie_category_kind AS ENUM ('NORMAL', 'NECESSARY', 'UNCATEGORISED');
+
+ALTER TABLE cookie_categories ADD COLUMN kind cookie_category_kind NOT NULL DEFAULT 'NORMAL';
+UPDATE cookie_categories SET kind = 'NECESSARY' WHERE required = TRUE;
+ALTER TABLE cookie_categories ALTER COLUMN kind DROP DEFAULT;
+
+DROP INDEX idx_cookie_categories_one_required_per_banner;
+ALTER TABLE cookie_categories DROP COLUMN required;
+
+CREATE UNIQUE INDEX idx_cookie_categories_one_necessary_per_banner
+    ON cookie_categories (cookie_banner_id) WHERE kind = 'NECESSARY';
+CREATE UNIQUE INDEX idx_cookie_categories_one_uncategorised_per_banner
+    ON cookie_categories (cookie_banner_id) WHERE kind = 'UNCATEGORISED';