Split zip volumes (.zNN) and .xNN as volumes, but not .x32/.x64/.x86

87e15d8's .[s-v]NN let "Licence 700790900887990.z18" and "….x31" uploads
fall apart again (+1,740 releases on the corpus). .zNN is a split zip volume;
.xNN is a volume unless it's a build.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/unit/release/identity.spec.ts

@@ -305,6 +305,9 @@ test.group('release / par2 names', () => {
     assert.equal(fileStem('the.office.us.s01.rar'), 'the.office.us.s01')
     assert.equal(fileStem('Some.Show.S01'), 'Some.Show.S01')
     assert.equal(fileStem('Electric.Rain.Swift.3D.PS.v1.0.142.x64'), 'Electric.Rain.Swift.3D.PS.v1.0.142.x64')
+    assert.equal(fileStem('App.x86'), 'App.x86')
+    assert.equal(fileStem('Licence 700790900887990.z18'), 'Licence 700790900887990')
+    assert.equal(fileStem('Licence 077887994400668.x12'), 'Licence 077887994400668')
     assert.equal(fileStem('chappelle1.part02.rev'), 'chappelle1')
     assert.equal(fileStem('chappelle1.rev'), 'chappelle1')
     assert.equal(fileStem('VwE3i90MVX9dqMFuDfzdS7Q6.part1.par2'), 'VwE3i90MVX9dqMFuDfzdS7Q6')