Fix: store KWallet passwords via D-Bus (kwallet-query -w never persists)

kwallet-query --write-password returns success but does not create the folder
or persist the secret, so saved host passwords were silently lost and share
enumeration failed with NT_STATUS_LOGON_FAILURE. Write/delete now go through
the kwalletd6 D-Bus API via qdbus6 (open/createFolder/writePassword). Reads
stay on kwallet-query (they work). Also drop smbclient -N (was forcing an
anonymous session) and silence KWallet read stderr. Adds qt6-tools dep.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

install.sh

@@ -33,6 +33,7 @@ check pkexec        "polkit"
 check mount.cifs    "cifs-utils"
 check smbclient     "smbclient"
 check kwallet-query "kwallet (KF6)"
+check qdbus6        "qt6-tools"
 check findmnt       "util-linux"
 if [ "$missing" -ne 0 ]; then
     warn "resolve the above and re-run. Continuing anyway..."