Admin-managed feedback categories

Categories move from a hard-coded list to a feedback_categories table
(migration 0062), seeded with the four existing keys, labels and
descriptions so production feedback is untouched; any other key already in
use gets an archived category. Keys are fixed, so renames relabel past
feedback. Archive hides a category from the form; only unused categories
can be deleted. Submissions are validated against active categories, and
feedback responses carry category_label.

New: GET /feedback/categories (public); /admin/feedback/categories CRUD +
reorder behind the new feedback:categories permission (granted to Admin).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/model/admin.go

@@ -89,6 +89,7 @@ type AdminCollection struct {
 type AdminFeedback struct {
 	ID             string     `json:"id"`
 	Category       string     `json:"category"`
+	CategoryLabel  string     `json:"category_label"`
 	Message        string     `json:"message"`
 	ContactEmail   *string    `json:"contact_email"`
 	CreatedAt      time.Time  `json:"created_at"`