Add automated PXE installation via ISO GRUB modification and auto-answer endpoint

Modifies uploaded ISO's GRUB config in-place to set timeout=0 and inject
proxmox-start-auto-installer + answer-url kernel params, enabling fully
hands-off installation. Adds /api/boot/auto-answer endpoint that identifies
hosts by ARP-resolving the requester's IP to MAC address.

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

internal/image/service.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"fmt"
 	"io"
+	"log"
 	"os"
 	"path/filepath"
 	"regexp"
@@ -13,8 +14,9 @@ import (
 )
 
 type Service struct {
-	Store    *store.Images
-	ImageDir string
+	Store     *store.Images
+	ImageDir  string
+	PublicURL string
 }
 
 type UploadParams struct {
@@ -53,6 +55,20 @@ func (s *Service) Upload(ctx context.Context, p UploadParams) (*model.Image, err
 		return nil, fmt.Errorf("extract ISO: %w", err)
 	}
 
+	if s.PublicURL != "" {
+		report := func(stage, detail string) {
+			if p.OnProgress != nil {
+				p.OnProgress(stage, detail)
+			}
+		}
+		report("packaging", "Configuring ISO for automated installation...")
+		isoFile := filepath.Join(destDir, result.ISOFilename)
+		answerURL := s.PublicURL + "/api/boot/auto-answer"
+		if err := ModifyISOForAutoInstall(isoFile, answerURL); err != nil {
+			log.Printf("image: ISO auto-install modification failed (non-fatal): %v", err)
+		}
+	}
+
 	kernelPath := filepath.Join(p.Name, result.KernelFilename)
 	initrdPath := filepath.Join(p.Name, result.InitrdFilename)
 	isoPath := filepath.Join(p.Name, result.ISOFilename)