fix(labels): replace incorrect ams_30x15 preset with correct AMS holder sizes (#1426)

Reporter — the same person who originally requested the labels
  feature in #809 — discovered that the ams_30x15 preset's 30x15 mm
  dimension didn't actually fit any variant of the MakerWorld AMS
  Filament Label Holder (model 752566) it advertised. Two new
  presets replace it:

  - ams_holder_74x33 (74 x 33 mm) matches the printable label STL
    bundled in the MakerWorld project
  - ams_holder_75x55 (75 x 55 mm) fits the cardstock-insert variant
    the reporter validated on bench

  Both cross the 20 mm height threshold so they land in the roomy
  layout branch — swatch on the left, QR on the right, multi-line
  text (brand, material, hex code, spool ID) in the middle. The
  old 30x15 mm preset couldn't fit a QR code; the new ones do.

  No DB migration: the preset name was never persisted. Callers
  scripting the old ams_30x15 value get a clean 422 at the route's
  Literal validator with the new valid values listed.

  i18n: replaced inventory.labels.templates.ams.{label,hint} with
  amsHolderSmall and amsHolderLarge across all 8 locales with real
  translations; parity guard cleaned of the stale English-fallback
  cognate entries. Parity holds at 4856 leaves per locale.

  Tests: backend label renderer + integration tests cover both new
  presets; LabelTemplatePickerModal test updated for the 6-button
  grid and the new template value in the API-call assertion.

backend/tests/integration/test_labels.py

@@ -66,7 +66,13 @@ class TestLocalInventoryLabels:
     @pytest.mark.integration
     async def test_all_four_templates_succeed(self, async_client: AsyncClient, spool_factory):
         s = await spool_factory()
-        for template in ("ams_30x15", "box_62x29", "avery_5160", "avery_l7160"):
+        for template in (
+            "ams_holder_74x33",
+            "ams_holder_75x55",
+            "box_62x29",
+            "avery_5160",
+            "avery_l7160",
+        ):
             resp = await async_client.post(
                 "/api/v1/inventory/labels",
                 json={"spool_ids": [s.id], "template": template},
@@ -100,7 +106,7 @@ class TestLocalInventoryLabels:
         s = await spool_factory()
         resp = await async_client.post(
             "/api/v1/inventory/labels",
-            json={"spool_ids": [s.id, 99999], "template": "ams_30x15"},
+            json={"spool_ids": [s.id, 99999], "template": "ams_holder_74x33"},
         )
         assert resp.status_code == 404
         assert "99999" in resp.text