Start with an empty document; offer Datei › Neu and Datei › Muster

A first start (nothing in localStorage) now opens a blank document -- one
sheet "Blatt 1" with an empty "Tabelle 1" -- instead of the pre-filled
sample. The file menu gets "Neu" (blank document) and "Muster ·
Umsatzanalyse" (the former seed), both behind a confirm and both starting
a fresh undo history. The toolbar's "Zurücksetzen" button is gone; its job
is now Datei › Muster.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/store/document.ts

@@ -77,7 +77,7 @@ import type {
   TextObject,
 } from './types';
 import { defaultTableView, DEFAULT_ROW_H, MIN_GRID_SIZE, MAX_GRID_SIZE } from './types';
-import { createSeedDocument } from '../data/seed';
+import { createBlankDocument, createSeedDocument } from '../data/seed';
 import { validateDocument } from '../io/json';
 
 const STORAGE_KEY = 'numolus:doc:v2';
@@ -535,7 +535,7 @@ function loadInitial(): DocumentState {
   } catch {
     /* missing / corrupt / stale-schema -> clean fallback */
   }
-  return createSeedDocument();
+  return createBlankDocument();
 }
 
 // ---- store singleton --------------------------------------------------
@@ -2848,6 +2848,11 @@ function createStore() {
     applyDocumentState(next);
     resetHistory();
   }
+  /** Datei › Neu: an empty document. */
+  function newDocument() {
+    replaceDocument(createBlankDocument());
+  }
+  /** Datei › Muster: the pre-filled sample document. */
   function resetToSeed() {
     replaceDocument(createSeedDocument());
   }
@@ -3040,6 +3045,7 @@ function createStore() {
     pointDrag,
     // document
     replaceDocument,
+    newDocument,
     resetToSeed,
     appendSheets,
     addTableFromCells,