fix: MODIFICA button now edits inventory instance (expiry/location/qty/vacuum)

The MODIFICA button on the action page was opening the catalog editor
(name/brand/category). Users expect it to edit the physical item in hand.

Changes:
- MODIFICA button → openInventoryEdit(): edits the inventory row directly.
  If product is in one location → opens editActionInventoryItem directly.
  If multiple locations → shows a location picker modal first.
- editActionInventoryItem modal already has: qty ±, unit, conf size, location
  buttons, expiry date, vacuum toggle — all fields for the instance.
- Catalog editing (name/brand/category) moved to a small secondary link
  '⚙️ Modifica scheda prodotto' shown discreetly below the action buttons.
- Removed redundant 'Tocca una riga per modificare' hint from status bar.
- Added .btn-link-small CSS class for the secondary catalog-edit link.

data/cron.log

@@ -1803,3 +1803,10 @@
 [2026-04-07 12:05:02] OK — 31 items cached
 [2026-04-07 12:10:01] OK — 30 items cached
 [2026-04-07 12:15:02] OK — 30 items cached
+[2026-04-07 12:20:02] OK — 32 items cached
+[2026-04-07 12:25:02] OK — 33 items cached
+[2026-04-07 12:30:02] OK — 33 items cached
+[2026-04-07 12:35:01] OK — 33 items cached
+[2026-04-07 12:40:02] OK — 33 items cached
+[2026-04-07 12:45:01] OK — 33 items cached
+[2026-04-07 12:50:02] OK — 33 items cached