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

package.json

@@ -1,6 +1,6 @@
 {
   "name": "markdown-converter",
-  "version": "4.11.0",
+  "version": "4.11.1",
   "description": "Professional Markdown editor and universal file converter with PDF editing, batch processing, and syntax highlighting",
   "main": "src/main.js",
   "scripts": {