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>

internal/store/images.go

@@ -93,6 +93,34 @@ func (s *Images) SetDefault(ctx context.Context, id int64) error {
 	return tx.Commit()
 }
 
+func (s *Images) GetByName(ctx context.Context, name string) (*model.Image, error) {
+	row := s.DB.QueryRowContext(ctx, `SELECT id, name, kind, version, kernel_path, initrd_path, is_default, created_at FROM images WHERE name = ?`, name)
+	var img model.Image
+	var isDefault int
+	var createdAt string
+	if err := row.Scan(&img.ID, &img.Name, &img.Kind, &img.Version, &img.KernelPath, &img.InitrdPath, &isDefault, &createdAt); err != nil {
+		if err == sql.ErrNoRows {
+			return nil, ErrNotFound
+		}
+		return nil, fmt.Errorf("get image by name: %w", err)
+	}
+	img.IsDefault = isDefault == 1
+	img.CreatedAt, _ = time.Parse(time.RFC3339, createdAt)
+	return &img, nil
+}
+
+func (s *Images) Delete(ctx context.Context, id int64) error {
+	res, err := s.DB.ExecContext(ctx, `DELETE FROM images WHERE id = ?`, id)
+	if err != nil {
+		return fmt.Errorf("delete image: %w", err)
+	}
+	n, _ := res.RowsAffected()
+	if n == 0 {
+		return ErrNotFound
+	}
+	return nil
+}
+
 func boolToInt(b bool) int {
 	if b {
 		return 1