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/booking_db.py

@@ -183,6 +183,27 @@ def update_resource(client_id, resource_id, **fields):
     return row
 
 
+def delete_resource(client_id, resource_id):
+    """Permanently remove a resource (and its resource_hours), scoped to
+    client_id. Returns resource_id on success, None if no such resource
+    exists for this client. Existing bookings against this resource_id are
+    left as-is (no FK, matching this schema's convention) -- the owner
+    agenda already falls back to showing the raw resource_id in place of a
+    name for a booking whose resource no longer resolves (see
+    owner_booking.py's _agenda_days), same as it does for a deactivated one."""
+    with db.connect() as conn, conn.cursor() as cur:
+        cur.execute(
+            "DELETE FROM resources WHERE client_id = %s AND resource_id = %s RETURNING resource_id",
+            (client_id, resource_id))
+        row = cur.fetchone()
+        if row is None:
+            conn.commit()
+            return None
+        cur.execute("DELETE FROM resource_hours WHERE resource_id = %s", (resource_id,))
+        conn.commit()
+    return row["resource_id"]
+
+
 def get_resource_hours(client_id, resource_id):
     """Return {weekday: (opens_at, closes_at)} for client_id's own resource
     (empty for a resource with no hours configured yet, or one that isn't