fix: update Linux bootable to Ubuntu 24.04.4, add format-persistence.sh, rewrite guide

- Update all 24.04.2 references to 24.04.4 (ISO name, URLs, SHA256, docs)
- Add format-persistence.sh to bootable/linux-setup/ (from working E: drive)
- Rewrite website guide.html Linux tutorial: Linux Mint + Rufus → Ventoy + Ubuntu

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

bootable/ventoy/ventoy.json

@@ -1,7 +1,7 @@
 {
   "persistence": [
     {
-      "image": "/ubuntu-24.04.2-desktop-amd64.iso",
+      "image": "/ubuntu-24.04.4-desktop-amd64.iso",
       "backend": "/persistence.dat",
       "autosel": 1
     }