Owner settings: add a real delete for Mitarbeiter (barbers)

Rename + active-toggle already existed (this session, earlier commit)
-- this adds a genuine, permanent delete alongside them, guarded by a
confirm() prompt that points to the "Aktiv" checkbox as the reversible
alternative for someone just temporarily off. Existing bookings against
a deleted resource are left as-is (no FK in this schema, matching its
existing convention) -- the owner agenda already falls back to the raw
resource_id for a booking whose resource no longer resolves, same as
it does today for a deactivated one.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

backoffice/app/owner_settings.py

@@ -168,6 +168,21 @@ def update_resource(resource_id):
     return _redirect()
 
 
+@bp.post("/resources/<resource_id>/delete")
+@login_required
+def delete_resource(resource_id):
+    """Permanently removes a barber (#21 follow-up). Past bookings against
+    them are untouched -- see booking_db.delete_resource's docstring -- so
+    this is a real delete, not just deactivation; the "Aktiv" checkbox on the
+    resource's own edit form is the softer, reversible alternative for
+    someone temporarily off (on leave, etc.)."""
+    client_id = session["client_id"]
+    deleted = bdb.delete_resource(client_id, resource_id)
+    if deleted is None:
+        return _redirect(error="not_found")
+    return _redirect()
+
+
 @bp.post("/resources/<resource_id>/hours")
 @login_required
 def update_resource_hours(resource_id):