perf(invoices): the invoice editor renders on the first paint from the session cache (#1937)

"Ny faktura" was the slowest form to fill in: the list page lazy-loaded
NewInvoiceDialog, which lazy-loaded InvoiceEditor (ssr:false), which then
issued four requests on mount (customers, articles, chart of accounts,
company settings) and hid the ENTIRE form behind a spinner until the
customers query alone resolved, even though the other three had landed.
Reopening the dialog paid all of it again.

- InvoiceEditor reads customers, articles, posting accounts and settings
  from lib/reference-data (seeded by the dashboard layout). The whole-form
  spinner gate is gone; the customer picker shows "Hämtar kunder ..." only
  while the list is genuinely uncached. Company settings are applied once
  per editor instance through a guarded effect, so a background
  revalidation can never re-run the create-mode prefills over notes or a
  reference the user has typed. Inline customer/article creation
  invalidates the shared cache (awaited, so the new option resolves before
  the line points at it). Customers now come through /api/customers, which
  masks the personnummer column; nothing in the editor rendered it.
- NewInvoiceDialog imports the editor statically: the dialog is itself a
  next/dynamic chunk on the list page, so this is one deferred chunk
  download when the dialog opens instead of two sequential ones.
- New strings: invoice_editor.loading_customers (sv + en).

Per "Ny faktura": 2 sequential chunk loads -> 1; blocking mount requests
4 -> 0 (cached) with every field populated on the first render.
raw-reference-fetch ratchet: 46 -> 45 files. SendInvoiceDialog and
PaymentBookingDialog (init() flows) stay in the baseline for a later PR.

Co-authored-by: Jakob Wennberg <311770904+jakobwennberg-oss@users.noreply.github.com>
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

messages/en.json

@@ -3758,6 +3758,7 @@
     "bank_add_now": "Add now",
     "customer_card_title": "Customer",
     "select_customer_placeholder": "Select customer",
+    "loading_customers": "Loading customers ...",
     "no_customers_yet": "No customers yet",
     "create_customer": "Create customer",
     "create_customer_dialog_title": "Add customer",

messages/sv.json

@@ -3758,6 +3758,7 @@
     "bank_add_now": "Lägg till nu",
     "customer_card_title": "Kund",
     "select_customer_placeholder": "Välj kund",
+    "loading_customers": "Hämtar kunder ...",
     "no_customers_yet": "Inga kunder än",
     "create_customer": "Skapa kund",
     "create_customer_dialog_title": "Lägg till kund",