Add slug to cookie categories for stable consent identifiers

The category slug provides a stable, URL-safe key used as the
data-cookie-consent attribute value and consent data key, replacing
the fragile category name. This prevents breakage when categories
are renamed.

- Add slug column with unique-per-banner constraint and backfill migration
- Add Slug validator (lowercase alphanumeric + hyphens)
- Propagate slug through GraphQL schema, service layer, and snapshot
- Update console UI with slug field in create/edit forms
- Switch cookie-banner widget to use slug as consent data keys

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

pkg/server/api/console/v1/cookie_banner_resolvers.go

@@ -419,6 +419,7 @@ func (r *mutationResolver) CreateCookieCategory(ctx context.Context, input types
 		cookiebanner.CreateCookieCategoryRequest{
 			CookieBannerID: input.CookieBannerID,
 			Name:           input.Name,
+			Slug:           input.Slug,
 			Description:    input.Description,
 			Rank:           input.Rank,
 		},
@@ -427,6 +428,9 @@ func (r *mutationResolver) CreateCookieCategory(ctx context.Context, input types
 		if errors.Is(err, cookiebanner.ErrBannerNotFound) {
 			return nil, gqlutils.NotFound(ctx, err)
 		}
+		if errors.Is(err, cookiebanner.ErrCategorySlugAlreadyExists) {
+			return nil, gqlutils.Conflict(ctx, err)
+		}
 		if validationErrors, ok := errors.AsType[validator.ValidationErrors](err); ok {
 			return nil, gqlutils.InvalidValidationErrors(ctx, validationErrors)
 		}
@@ -460,6 +464,7 @@ func (r *mutationResolver) UpdateCookieCategory(ctx context.Context, input types
 		cookiebanner.UpdateCookieCategoryRequest{
 			CookieCategoryID: input.CookieCategoryID,
 			Name:             input.Name,
+			Slug:             input.Slug,
 			Description:      input.Description,
 		},
 	)
@@ -467,6 +472,9 @@ func (r *mutationResolver) UpdateCookieCategory(ctx context.Context, input types
 		if errors.Is(err, cookiebanner.ErrCategoryNotFound) {
 			return nil, gqlutils.NotFound(ctx, err)
 		}
+		if errors.Is(err, cookiebanner.ErrCategorySlugAlreadyExists) {
+			return nil, gqlutils.Conflict(ctx, err)
+		}
 		if validationErrors, ok := errors.AsType[validator.ValidationErrors](err); ok {
 			return nil, gqlutils.InvalidValidationErrors(ctx, validationErrors)
 		}