feat(fase-5.10.0): drop shopping_items.unit column

The unit field had no edit path under the redesign (only name + qty
remain in the row; the double-tap overlay is name-only). Users can encode
the unit inside the name when it matters — e.g. "Milk 1L", "Eggs 1 doz".

Changes
  supabase/migrations/011_drop_shopping_items_unit.sql — DROP COLUMN
  supabase/seed.sql — unit values folded into names where relevant
  supabase/tests/002_item_frequency_trigger.sql — remove unit from INSERT
  packages/types — remove unit from ShoppingItem Row/Insert/Update
  apps/web/src/lib/stores/lists.ts — addItem/updateItem signatures
  apps/web/src/routes/(app)/lists/[id]/+page.svelte — purge newUnit /
    editUnit state + inputs + display
  apps/web/src/routes/(app)/lists/[id]/session/+page.svelte — simplify
    quantity-only render
  apps/web/messages/{en,es}.json — remove list_unit_label

Verification
  just test-db  → 34 pgTAP green
  just test-integration → 140 + 2 skipped
  just test-unit → 11 green
  just test-e2e → 39 + 2 skipped

The generated search tsvector on shopping_items.search already indexes
only `name`, so full-text search coverage is unchanged.

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

supabase/tests/002_item_frequency_trigger.sql

@@ -23,8 +23,8 @@ VALUES (
 ) ON CONFLICT (id) DO NOTHING;
 
 -- D-13: Inserting an item creates a new frequency row (normalized name)
-INSERT INTO public.shopping_items (list_id, name, quantity, unit, sort_order, created_by)
-VALUES ('cccccccc-cccc-cccc-cccc-cccccccccccc', '  Butter  ', 1, NULL, 50, '11111111-1111-1111-1111-111111111111');
+INSERT INTO public.shopping_items (list_id, name, quantity, sort_order, created_by)
+VALUES ('cccccccc-cccc-cccc-cccc-cccccccccccc', '  Butter  ', 1, 50, '11111111-1111-1111-1111-111111111111');
 
 SELECT ok(
     EXISTS (