fix(invoice): drop salutation from PDF (it's an invoice, not a letter)

The 'Hallo,' (DE) / 'Dear Sir or Madam,' (EN) line above the items
table was leftover letter framing. Removing it:
  - reclaims a bit of vertical space at the top of every PDF, and
  - sidesteps the formal-vs-informal tone debate entirely \u2014 a tax
    document doesn't need a greeting.

The 'Vielen Dank f\u00fcr deine Bestellung. Wir stellen dir hiermit
folgendes in Rechnung:' / 'Thank you for your order. We hereby
invoice you for the following:' line is kept as it actually
introduces the items table.

Smoke assertions flipped from 'must contain Hallo,' to 'must NOT
contain Hallo, / Sehr geehrte …' so the suppression is enforced
in CI.

scripts/render-sample.ts

@@ -544,8 +544,11 @@ async function main() {
 
   // Informal German tone (du/dein) — make sure no formal "Sie/Ihren" remains
   // in the strings we control (footer / signature lines come from settings).
-  assert("DE PDF uses informal salutation 'Hallo,'", deText.includes("Hallo,"));
-  assert("DE PDF no longer uses 'Sehr geehrte Damen und Herren'", !deText.includes("Sehr geehrte Damen und Herren"));
+  // The PDF intentionally has NO salutation — this is an invoice, not a
+  // letter. Both formal ("Sehr geehrte …") and informal ("Hallo,") are
+  // suppressed.
+  assert("DE PDF has no 'Hallo,' salutation", !deText.includes("Hallo,"));
+  assert("DE PDF has no 'Sehr geehrte Damen und Herren' salutation", !deText.includes("Sehr geehrte Damen und Herren"));
   assert("DE PDF uses informal 'deine Bestellung'", deText.includes("deine Bestellung"));
   assert(
     "DE PDF payment-terms uses informal 'überweise … für dich'",