chore: ignore .DS_Store, remove from tracking, fix genapkovl path in build, udhcpc background mode

- add .DS_Store to .gitignore and remove tracked files
- copy genapkovl-bee_debug.sh to /var/tmp before mkimage (was causing "no such file" error)
- switch udhcpc to background mode (-b -t 0) so network comes up when cable connected after boot
- add -B to DROPBEAR_OPTS to allow password fallback (bee/eeb)

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

.gitignore

@@ -1,3 +1,4 @@
 .env
+.DS_Store
 dist/
 iso/out/