fix: skip external MariaDB repo on trixie, clean stale repo files

- Trixie uses native Debian mariadb packages (external repo has no
  trixie release), so wo_mysql_repo is empty and repo add is skipped
- Clean up old openlitespeed.list and mariadb.list during install so
  they get regenerated with correct GPG keyring paths

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

wo/core/variables.py

@@ -172,6 +172,9 @@ class WOVar():
         "mariadb-common", "python3-mysqldb"]
     if wo_distro == 'raspbian':
         mariadb_ver = '10.3'
+    elif wo_platform_codename == 'trixie':
+        mariadb_ver = ''
+        wo_mysql = wo_mysql + ["mariadb-backup"]
     else:
         mariadb_ver = '11.4'
         wo_mysql = wo_mysql + ["mariadb-backup"]
@@ -182,9 +185,13 @@ class WOVar():
     wo_clamav = ["clamav", "clamav-freshclam"]
 
     # APT repositories
-    wo_mysql_repo = ("deb [signed-by=/etc/apt/keyrings/mariadb-keyring.pgp] "
-                     "http://deb.mariadb.org/"
-                     f"{mariadb_ver}/{wo_distro} {wo_platform_codename} main")
+    if mariadb_ver:
+        wo_mysql_repo = ("deb [signed-by=/etc/apt/keyrings/mariadb-keyring.pgp] "
+                         "http://deb.mariadb.org/"
+                         f"{mariadb_ver}/{wo_distro} {wo_platform_codename} main")
+    else:
+        # trixie: use native Debian mariadb packages, no external repo
+        wo_mysql_repo = ""
     mariadb_repo_key = "https://mariadb.org/mariadb_release_signing_key.pgp"
     if wo_distro == 'ubuntu':
         # LSPHP comes from LiteSpeed repo (same as OLS)