feat: add the DIN 5008 Form A letter template

The norm defines two business-letter forms and only Form B existed. Both
now come out of one builder parameterized by where the address field opens,
27mm for Form A against 45mm for Form B. Measured headlessly: 26.98 and
44.97mm, their info blocks at 31.99 and 49.98mm, the info column at
124.99mm. The gallery draws Form A's address field higher, or the two
cards would be indistinguishable.

src/lib/components/CLAUDE.md

@@ -207,10 +207,15 @@ size alone makes a short word far too small and a long one overflow the page.
 `App.svelte`'s `applyTemplate` — `resetDocumentState()` (the extracted body of New),
 then the template's content, margins, styles and fold marks. `documentName` becomes the
 localized template name and no file handle is bound, so the first Save asks where. The
-DIN letter's mm positions were verified headlessly (45mm address field, 125mm info
-column); its module documents the arithmetic. The letter-family templates share that
-geometry (and the JSON builders) via `templates/builders.ts`; `tests/unit/templates.test.ts`
-schema-checks every entry in both locales.
+norm's two DIN letter forms come out of one builder in `din5008.ts`, parameterized by
+where the address field opens; both were verified headlessly — Form B 44.97mm, Form A
+26.98mm, their info blocks 49.98/31.99mm, the info column 124.99mm. The letter-family
+templates share that geometry (and the JSON builders) via `templates/builders.ts`;
+`tests/unit/templates.test.ts` schema-checks every entry in both locales.
+
+A block's rect starts **above** its own first line — the spacing model puts space-before
+inside the box — so a probe measuring these positions must range-select the text, not
+read `getBoundingClientRect()` on the paragraph.
 
 ## Fold marks (`FoldMarkLayer.svelte`, `storage/foldMarks.ts`)
 

src/lib/components/TemplateGalleryDialog.svelte

@@ -64,9 +64,11 @@
               <span class="fold f1"></span>
               <span class="fold f2"></span>
             {:else}
-              <span class="addr"></span>
-              {#if entry.id === 'din5008b'}
-                <span class="info"></span>
+              <!-- Form A opens its address field 18mm higher, which is the only thing
+                   telling the two DIN cards apart. -->
+              <span class="addr" class:high={entry.id === 'din5008a'}></span>
+              {#if entry.id.startsWith('din5008')}
+                <span class="info" class:high={entry.id === 'din5008a'}></span>
               {:else}
                 <span class="date"></span>
               {/if}
@@ -183,6 +185,7 @@
   }
   .addr { top: 26px; left: 12px; width: 28px; height: 16px; }
   .info { top: 26px; left: 52px; width: 22px; height: 16px; }
+  .addr.high, .info.high { top: 15px; }
   .date { top: 48px; right: 12px; width: 20px; height: 3px; }
   .line { left: 12px; height: 3px; }
   .l1 { top: 56px; width: 40px; background: #8a94a0; }

src/lib/i18n/locales/de.ts

@@ -689,8 +689,12 @@ const de: Messages = {
   templates: {
     title: 'Neu aus Vorlage',
     din5008b: {
-      name: 'Brief nach DIN 5008',
-      description: 'Geschäftsbrief (Form B): Anschriftfeld fürs Fensterkuvert, Infoblock, Falzmarken.',
+      name: 'Brief nach DIN 5008 (Form B)',
+      description: 'Geschäftsbrief mit vollem Briefkopf: Anschriftfeld fürs Fensterkuvert ab 45 mm, Infoblock, Falzmarken.',
+    },
+    din5008a: {
+      name: 'Brief nach DIN 5008 (Form A)',
+      description: 'Geschäftsbrief mit einzeiligem Briefkopf: Anschriftfeld ab 27 mm, Infoblock, Falzmarken — 18 mm mehr Text auf Seite 1.',
     },
     privateLetter: {
       name: 'Privatbrief',

src/lib/i18n/locales/en.ts

@@ -695,8 +695,12 @@ const en = {
   templates: {
     title: 'New from template',
     din5008b: {
-      name: 'DIN 5008 letter',
-      description: 'Business letter (Form B): address field for a window envelope, info block, fold marks.',
+      name: 'DIN 5008 letter (Form B)',
+      description: 'Business letter with a full letterhead: address field for a window envelope from 45 mm, info block, fold marks.',
+    },
+    din5008a: {
+      name: 'DIN 5008 letter (Form A)',
+      description: 'Business letter with a one-line letterhead: address field from 27 mm, info block, fold marks — 18 mm more text on page 1.',
     },
     privateLetter: {
       name: 'Personal letter',

src/lib/templates/din5008.ts

@@ -2,17 +2,17 @@ import { t } from '../i18n/i18n.svelte';
 import type { TemplateData, TemplateEntry } from './types';
 import { BOLD, LINE_PT, MM_TO_PT, P, PLH, RETURN_SPACE_AFTER_PT, SMALL, T, dateField, type N } from './builders';
 
-// DIN 5008 Form B business letter. All vertical positions are paragraph rhythm from a
-// 20mm top margin at 12pt single spacing (one line ≈ 4.87mm); the mm targets below
-// are the norm's.
+// The two DIN 5008 business-letter forms, differing only in where the address field
+// opens: Form A at 27mm (a one-line letterhead), Form B at 45mm (a full one). Vertical
+// positions are paragraph rhythm from a 20mm top margin at 12pt (one line ≈ 4.87mm).
 
-// 45mm target − 20mm margin − one letterhead line.
-const RETURN_SPACE_BEFORE_PT = Math.round((45 - 20) * MM_TO_PT - LINE_PT);
 // Info block at 125mm from the paper edge = 10cm from the 25mm text margin.
 const INFO_TAB = '10l';
 
-function buildLetter(): TemplateData {
+function buildLetter(headMm: number): TemplateData {
   const L = t().templates.letter;
+  // The address field's mm target − the 20mm margin − one letterhead line.
+  const returnSpaceBefore = Math.round((headMm - 20) * MM_TO_PT - LINE_PT);
   // An info line with no address half indents to the column instead of leading with
   // a tab (a tab with nothing before it stays on the default grid).
   const addressRow = (attrs: N | null, addr: N[], info: N[]): N =>
@@ -26,9 +26,9 @@ function buildLetter(): TemplateData {
       type: 'doc',
       content: [
         P(null, PLH(L.companyName, BOLD)),
-        // The one-line return address opens the address field at 45mm from the top.
+        // The one-line return address opens the address field at its mm target.
         // 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)),
+        P({ spaceBefore: returnSpaceBefore, spaceAfter: RETURN_SPACE_AFTER_PT, fontSize: '8pt' }, PLH(L.returnAddress, SMALL)),
         // 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)]),
@@ -59,5 +59,12 @@ export const din5008b: TemplateEntry = {
   id: 'din5008b',
   name: () => t().templates.din5008b.name,
   description: () => t().templates.din5008b.description,
-  build: buildLetter,
+  build: () => buildLetter(45),
+};
+
+export const din5008a: TemplateEntry = {
+  id: 'din5008a',
+  name: () => t().templates.din5008a.name,
+  description: () => t().templates.din5008a.description,
+  build: () => buildLetter(27),
 };

src/lib/templates/registry.ts

@@ -1,4 +1,4 @@
-import { din5008b } from './din5008b';
+import { din5008a, din5008b } from './din5008';
 import { privateLetter } from './privateLetter';
 import { coverLetter } from './coverLetter';
 import { cv } from './cv';
@@ -7,7 +7,7 @@ import { minutes } from './minutes';
 import type { TemplateEntry } from './types';
 
 // What the gallery offers.
-export const TEMPLATES: TemplateEntry[] = [din5008b, privateLetter];
+export const TEMPLATES: TemplateEntry[] = [din5008b, din5008a, privateLetter];
 
 // Drafts kept compiling and tested but not selectable; move up once settled.
 export const SHELVED: TemplateEntry[] = [coverLetter, cv, invoice, minutes];