Image sets: suffixes that don't count the images go first

The set bound cut at an image name's last number, but in many threads
that's a suffix, so every image was a set ("It does my heart good to see
Red Dog dancing again": 4,683 releases of 4,730 files): a repeat of the
index (katelg010_10), a year (hgrscans1097_2009), a size
(pj02kristina_24of40_1600), an "of" total (24of40). imageSet drops
those, then cuts at the last number (cutie-071-032 stays cutie-071-).
Both implementations; tests; fixtures identical.

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

tests/unit/release/identity.spec.ts

@@ -222,6 +222,22 @@ test.group('release / par2 names', () => {
     assert.equal(mint('JimAndJoey Kindly Husband-to-Be.JPG').key, mint('Oops OnlyOneMore.JPG').key)
   })
 
+  test("an image's set: suffixes that don't count the images go first", async ({ assert }) => {
+    const { imageSet } = await import('#lib/release/identity')
+    for (const [stem, set] of [
+      ['stp250x001', 'stp250x'],
+      ['cutie-071-032', 'cutie-071-'],
+      ['katelg010_10', 'katelg'],
+      ['kate112lg035_35', 'kate112lg'],
+      ['!!hgrscans1097_2009', '!!hgrscans'],
+      ['pj02kristina_24of40_1600', 'pj02kristina_'],
+      ['keira_s04_l keira_s04_0040_l', 'keira_s04_l keira_s04_'],
+      ['IMG_2676', 'IMG_'],
+      ['2877-041', '2877-'],
+      ['JimAndJoey Kindly Husband-to-Be', ''],
+    ]) assert.equal(imageSet(stem), set, stem)
+  })
+
   test('dates are no file counters', async ({ assert }) => {
     const { counterTotal } = await import('#lib/release/identity')
     assert.isUndefined(counterTotal('Avira AntiVir Rescue System 08-29-2011.rar'))