fix(backup,restore): make restore drills replayable and leave swarm tasks alone

Restore fixes, both hit by the infinito svc-bkp e2e drill:

- mariadb --empty dropped tables one docker exec at a time with SET
  FOREIGN_KEY_CHECKS=0 issued in a separate client session, so the
  session-scoped toggle never applied and any FK-referenced parent table
  (mailu.users) died with ERROR 1451. Issue the toggle and all DROPs in
  one session.
- postgres --empty now drops only current_user-owned objects (extension
  members like pg_trgm's set_limit are superuser-owned) with IF EXISTS
  absorbing CASCADE fallout, and the replay skips superuser-only dump
  lines (COMMENT ON EXTENSION, ALTER DEFAULT PRIVILEGES) that abort an
  app-user psql run under ON_ERROR_STOP.

Backup fixes:

- pg_dump now runs with --no-owner --no-privileges so future dumps are
  replayable by the owning app user in the first place.
- Swarm task containers are never stopped or started manually: the
  orchestrator replaces a stopped task and a later docker start fails on
  the detached overlay network. filter_stoppable skips them visibly and
  the whitelist stop check ignores them.

Validated end to end against a live infinito compose stack: the full
svc-bkp-volume-2-local drill (verify, restore cycle, sql replay for
mailu, keycloak and one more db) passes with these patches applied.

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

src/baudolo/restore/db/mariadb.py

@@ -47,18 +47,6 @@ def restore_mariadb_sql(
         # IMPORTANT:
         # Do NOT hardcode 'mysql' here. Use the detected client.
         # MariaDB 11 images may not contain the mysql binary at all.
-        docker_exec(
-            container,
-            [
-                client,
-                "-u",
-                user,
-                f"--password={password}",
-                "-e",
-                "SET FOREIGN_KEY_CHECKS=0;",
-            ],
-        )
-
         result = docker_exec(
             container,
             [
@@ -74,7 +62,16 @@ def restore_mariadb_sql(
         )
         tables = result.stdout.decode().split()
 
-        for tbl in tables:
+        if tables:
+            # SET FOREIGN_KEY_CHECKS is session-scoped, so it must share one
+            # client session with the DROPs or FK constraints still fire.
+            drop_sql = (
+                "SET FOREIGN_KEY_CHECKS=0; "
+                + " ".join(
+                    f"DROP TABLE IF EXISTS `{db_name}`.`{tbl}`;" for tbl in tables
+                )
+                + " SET FOREIGN_KEY_CHECKS=1;"
+            )
             docker_exec(
                 container,
                 [
@@ -83,22 +80,10 @@ def restore_mariadb_sql(
                     user,
                     f"--password={password}",
                     "-e",
-                    f"DROP TABLE IF EXISTS `{db_name}`.`{tbl}`;",
+                    drop_sql,
                 ],
             )
 
-        docker_exec(
-            container,
-            [
-                client,
-                "-u",
-                user,
-                f"--password={password}",
-                "-e",
-                "SET FOREIGN_KEY_CHECKS=1;",
-            ],
-        )
-
     with open(sql_path, "rb") as f:
         docker_exec(
             container, [client, "-u", user, f"--password={password}", db_name], stdin=f