Add Electron UI replacing Flet gui.py

- electron/main.js: IPC handlers for config, credentials, Canvas API,
  subprocess management (node-pty on Unix for tqdm \r refresh), ML venv
  installer with CUDA detection, script constant read/write
- electron/preload.js: contextBridge exposes window.api to renderer
- electron/renderer/: single-page app with all 7 pages (Dashboard,
  Pipeline, Download, Transcribe, Align, Generate, Settings) matching
  gui.py behavior; dark teal theme; pinned terminal panel with 500-line
  cap and in-place \r refresh
- electron/test/main.test.js: 26 unit tests (config, constants,
  torchIndexUrl, getFilesStatus) — all passing
- gui.py kept intact; Electron is the new primary UI entrypoint

Author: nodeeeeee

.gitignore

@@ -33,3 +33,5 @@ config.json
 # ── Misc ──────────────────────────────────────────────────────────────────────
 *.egg-info/
 .DS_Store
+electron/node_modules/
+electron/package-lock.json