v0.16.0 — HomeBox CSV import + sold lifecycle + custom fields

Bring an existing HomeBox inventory straight in, and capture the fields HomeBox
has that we were missing (skipping asset IDs per Tony).

- Item: soldTo/soldPrice/soldDate/soldNotes + flexible customFields (JSON, e.g.
  VIN / oil weight for vehicles); both editable in the item dialog and shown on
  the detail page
- Pure HomeBox CSV parser (src/lib/inventory/homebox-import.ts, +5 tests) —
  RFC4180 quoting (commas/newlines/escaped quotes in fields), HomeBox's 0001-*
  null dates and 0 = empty price, semicolon labels, HB.field.* custom columns,
  nested 'A / B' location paths
- Import service + /api/v1/items/import: find-or-creates the nested locations
  and labels, creates items, recomputes location paths, returns a summary
- Inventory 'Import' button: paste/upload CSV, review every row with checkboxes
  (uncheck to skip), then import. Preview parses client-side (parser is pure)
- Verified end-to-end: nested locations, split labels, sold + custom fields,
  skip, quoted names, null-date handling. tsc + 38 tests + build green

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

prisma/schema.prisma

@@ -325,6 +325,15 @@ model Item {
   modelNumber      String?
   brand            String?   // brand / manufacturer
 
+  // Sold lifecycle (HomeBox parity)
+  soldTo       String?
+  soldPrice    Decimal?  @db.Decimal(10, 2)
+  soldDate     DateTime?
+  soldNotes    String?
+
+  // Custom fields — flexible key/value (e.g. VIN, "Oil Weight": "5W-30")
+  customFields Json?
+
   // Consumable attributes (Pantry phase)
   barcode        String?
   bestBefore     DateTime?