Add boot image management with ISO extraction and serving

Upload Proxmox ISOs via API or dashboard UI, extract kernel+initrd
using pure-Go iso9660 library, store on disk, and serve over HTTP
for PXE booting. Dynamic kernel/initrd filenames per image replace
the previous hardcoded paths.

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

.gitignore

@@ -25,3 +25,4 @@ vendor/
 
 # Templ generated
 *_templ.go
+.claude/settings.json