test(e2e): SPOT db images, PG18 mount layout, drop removed flags

Add a single source of truth in tests/e2e/helpers.py for the database
images and their in-container data dirs (POSTGRES_IMAGE=postgres:alpine,
POSTGRES_DATA_DIR=/var/lib/postgresql, MARIADB_IMAGE=mariadb:latest,
MARIADB_DATA_DIR=/var/lib/mysql) and route every test through it.
postgres:alpine now tracks 18+, which refuses a mount at
/var/lib/postgresql/data and stores data under /var/lib/postgresql, so
the mounts and the marker path move there. Drop the --rsync-image and the
renamed hard-restart flag from the invocations.

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

tests/e2e/helpers.py

@@ -7,6 +7,14 @@ import time
 import uuid
 from pathlib import Path
 
+# SPOT for the database images and their in-container data dirs the e2e
+# suite runs against. postgres:alpine tracks latest (18+), which mounts at
+# /var/lib/postgresql (not /var/lib/postgresql/data); bump here only.
+POSTGRES_IMAGE = "postgres:alpine"
+POSTGRES_DATA_DIR = "/var/lib/postgresql"
+MARIADB_IMAGE = "mariadb:latest"
+MARIADB_DATA_DIR = "/var/lib/mysql"
+
 
 def run(
     cmd: list[str],
@@ -172,7 +180,7 @@ def backup_run(
         "baudolo",
         "--compose-dir",
         compose_dir,
-        "--docker-compose-hard-restart-required",
+        "--hard-compose-restart",
         "mailu",
         "--repo-name",
         repo_name,