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/validator/validator_format.go

@@ -15,6 +15,7 @@
 package validator
 
 import (
+	"fmt"
 	"net/url"
 	"regexp"
 	"slices"
@@ -25,6 +26,7 @@ import (
 
 var (
 	domainRegex = regexp.MustCompile(`^(?:[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?\.)*[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?$`)
+	slugRegex   = regexp.MustCompile(`^[a-z0-9]+(-[a-z0-9]+)*$`)
 )
 
 // URL validates that a string is a valid URL with http or https scheme.
@@ -177,6 +179,36 @@ func Origin() ValidatorFunc {
 	}
 }
 
+// Slug validates that a string is a lowercase alphanumeric slug (with hyphens, no
+// leading/trailing hyphens, no consecutive hyphens) and does not exceed maxLen.
+func Slug(maxLen int) ValidatorFunc {
+	return func(value any) *ValidationError {
+		actualValue, isNil := dereferenceValue(value)
+		if isNil {
+			return nil
+		}
+
+		str, ok := actualValue.(string)
+		if !ok {
+			return newValidationError(ErrorCodeInvalidFormat, "value must be a string")
+		}
+
+		if str == "" {
+			return nil
+		}
+
+		if len(str) > maxLen {
+			return newValidationError(ErrorCodeTooLong, fmt.Sprintf("slug must be at most %d characters", maxLen))
+		}
+
+		if !slugRegex.MatchString(str) {
+			return newValidationError(ErrorCodeInvalidFormat, "slug must contain only lowercase letters, numbers, and hyphens")
+		}
+
+		return nil
+	}
+}
+
 // Domain validates that a string is a valid domain name.
 func Domain() ValidatorFunc {
 	return func(value any) *ValidationError {