feat(mx): upgrade PostgreSQL 14 → 16 and remove migration script

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

systems/x86_64-linux/mx/postgresql.nix

@@ -6,35 +6,6 @@
 }:
 {
   services.postgresql = {
-    package = pkgs.postgresql_14;
+    package = pkgs.postgresql_16;
   };
-
-  # Temporary: upgrade script for PostgreSQL 14 → 16 migration.
-  # After upgrading, change package above to postgresql_16 and remove this block.
-  environment.systemPackages = [
-    (
-      let
-        newPostgres = pkgs.postgresql_16;
-        cfg = config.services.postgresql;
-      in
-      pkgs.writeScriptBin "upgrade-pg-cluster" ''
-        set -eux
-        systemctl stop postgresql
-
-        export NEWDATA="/var/lib/postgresql/${newPostgres.psqlSchema}"
-        export NEWBIN="${newPostgres}/bin"
-        export OLDDATA="${cfg.dataDir}"
-        export OLDBIN="${cfg.finalPackage}/bin"
-
-        install -d -m 0700 -o postgres -g postgres "$NEWDATA"
-        cd "$NEWDATA"
-        sudo -u postgres "$NEWBIN/initdb" -D "$NEWDATA" ${lib.escapeShellArgs cfg.initdbArgs}
-
-        sudo -u postgres "$NEWBIN/pg_upgrade" \
-          --old-datadir "$OLDDATA" --new-datadir "$NEWDATA" \
-          --old-bindir "$OLDBIN" --new-bindir "$NEWBIN" \
-          "$@"
-      ''
-    )
-  ];
 }