feat: add the notation zone to the Form B letter

Two lines above the address (DIN's Zusatz- und Vermerkzone, filled
bottom-up) share their rows with the top of the info block, which now
starts at the norm's 50mm; the lower line carries a notation
placeholder (e.g. registered mail). Measured headlessly: info block
at 50.0mm, notation 54.8mm, address zone from 59.7mm ending 79mm —
inside the window.

src/lib/i18n/locales/de.ts

@@ -702,6 +702,7 @@ const de: Messages = {
       phoneNumber: 'Nummer',
       emailAddress: 'Adresse',
       place: 'Ort',
+      remark: 'Vermerk (z. B. Einschreiben)',
       subject: 'Betreff',
       salutation: 'Anrede',
       bodyText: 'Brieftext',

src/lib/i18n/locales/en.ts

@@ -708,6 +708,7 @@ const en = {
       phoneNumber: 'Number',
       emailAddress: 'Address',
       place: 'Place',
+      remark: 'Notation (e.g. registered mail)',
       subject: 'Subject',
       salutation: 'Salutation',
       bodyText: 'Letter text',

src/lib/templates/din5008b.ts

@@ -42,12 +42,14 @@ function buildLetter(): TemplateData {
         // The one-line return address opens the address field at 45mm from the top.
         // fontSize also shrinks the paragraph mark, so the line box is 8pt tall.
         P({ spaceBefore: RETURN_SPACE_BEFORE_PT, spaceAfter: RETURN_SPACE_AFTER_PT, fontSize: '8pt' }, PLH(L.returnAddress, SMALL)),
-        addressRow(null, [PLH(L.recipientCompany)], [T(L.yourRef), PLH(L.reference)]),
-        addressRow(null, [PLH(L.recipientName)], [T(L.yourMessage), PLH(L.date)]),
-        addressRow(null, [PLH(L.recipientStreet)], [T(L.ourRef), PLH(L.reference)]),
-        addressRow(null, [PLH(L.recipientCity)], [T(L.phone), PLH(L.phoneNumber)]),
-        addressRow(null, [], [T(L.email), PLH(L.emailAddress)]),
-        addressRow(null, [], [T(L.dateLabel), date]),
+        // Two notation lines above the address (DIN's Zusatz- und Vermerkzone, filled
+        // bottom-up), sharing their rows with the top of the info block.
+        addressRow(null, [], [T(L.yourRef), PLH(L.reference)]),
+        addressRow(null, [PLH(L.remark)], [T(L.yourMessage), PLH(L.date)]),
+        addressRow(null, [PLH(L.recipientCompany)], [T(L.ourRef), PLH(L.reference)]),
+        addressRow(null, [PLH(L.recipientName)], [T(L.phone), PLH(L.phoneNumber)]),
+        addressRow(null, [PLH(L.recipientStreet)], [T(L.email), PLH(L.emailAddress)]),
+        addressRow(null, [PLH(L.recipientCity)], [T(L.dateLabel), date]),
         P(null),
         P(null),
         P(null, PLH(L.subject, BOLD)),