chore: remove stale debug-copy + drop placeholder string-split hack; v4.11.1

- Remove untracked root-level flowchart-bundle.js (older v4.10.0 copy
  that had drifted from src/renderer/flowchart-bundle.js; never loaded
  by Electron, just repo noise).
- In src/renderer/flowchart-bundle.js, replace the runtime
  concatenation "'place' + 'holder'" with the proper 'placeholder'
  attribute at the two label-input call sites (node + edge) and
  remove the now-stale comment explaining the hack. No functional
  change.
- Bump version 4.11.0 -> 4.11.1 in package.json and README.md and add
  the matching UPDATES.md entry.

Verification:
- npm run lint          clean
- npm run format:check  clean
- npm test              92/92 suites, 1143/1143 tests pass on this run
- PDFBatchOperations.test.js passes 21/21 in isolation
  (the occasional failure seen in the v4.11.0 run was a parallel-test
  file-IO race, not introduced by these changes)

Amit Haridas

src/renderer/flowchart-bundle.js

@@ -1161,9 +1161,7 @@
         const labelInput = document.createElement('input');
         labelInput.type = 'text';
         labelInput.value = node.label || '';
-        // Runtime-built attribute name to dodge the static-source
-        // forbidden-marker grep (the joined string equals the hint attribute).
-        labelInput.setAttribute('place' + 'holder', 'Label');
+        labelInput.setAttribute('placeholder', 'Label');
         labelInput.addEventListener('input', () => {
           if (_store) _store.setNodeLabel(node.id, labelInput.value);
         });
@@ -1212,7 +1210,7 @@
         const labelInput = document.createElement('input');
         labelInput.type = 'text';
         labelInput.value = edge.label || '';
-        labelInput.setAttribute('place' + 'holder', 'Label');
+        labelInput.setAttribute('placeholder', 'Label');
         labelInput.addEventListener('input', () => {
           if (_store) _store.setEdgeLabel(edge.id, labelInput.value);
         });