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.

app/services/invoice/pdf/InvoiceDocument.tsx

@@ -390,7 +390,10 @@ export function InvoiceDocument({ invoice }: DocProps) {
             : ""}
         </Text>
 
-        <Text style={styles.paragraph}>{t.salutationGeneric}</Text>
+        {/* No salutation here on purpose — this is an invoice, not a
+         *  letter. Dropping the line saves vertical space and avoids
+         *  the formal/informal "Hallo," vs "Dear Sir or Madam" framing
+         *  that doesn't belong on a tax document. */}
         <Text style={styles.paragraph}>{t.thankYouLine}</Text>
 
         <View style={styles.table}>