Rename project from numbers-study to numolus

- package.json / package-lock.json: package name "numolus"
- README: new title, drop the "Case- und Designstudie" framing, update
  test count (331 -> 528)
- localStorage keys renamed to numolus:doc:v2 / numolus:theme; the old
  numbers-study:* keys are still read as a fallback so existing documents
  and theme choices survive the rename

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

src/store/document.ts

@@ -80,7 +80,9 @@ import { defaultTableView, DEFAULT_ROW_H, MIN_GRID_SIZE, MAX_GRID_SIZE } from '.
 import { createSeedDocument } from '../data/seed';
 import { validateDocument } from '../io/json';
 
-const STORAGE_KEY = 'numbers-study:doc:v2';
+const STORAGE_KEY = 'numolus:doc:v2';
+/** Key used before the rename to numolus -- still read as a fallback. */
+const LEGACY_STORAGE_KEY = 'numbers-study:doc:v2';
 
 const CASCADE = 28; // px offset for successive inserted objects
 
@@ -523,7 +525,8 @@ function rewriteRefsForRename(
 
 function loadInitial(): DocumentState {
   try {
-    const raw = localStorage.getItem(STORAGE_KEY);
+    const raw =
+      localStorage.getItem(STORAGE_KEY) ?? localStorage.getItem(LEGACY_STORAGE_KEY);
     if (raw) {
       // validateDocument migrates v1, validates + *normalises* v2 (fills in
       // `view` and other defaults for documents saved by an older build).