Fix #221: image pastes scale to fit, no code box, accurate size, raw serves image

- paste view: image attachments render in a scalable preview (max-height
  min(70vh, 720px), object-fit contain) and the code box is omitted;
  wrap/copy buttons hidden for image pastes
- SizeHuman/stats summary show the attachment size for file pastes
  (row.Content is empty for file pastes, was showing 0 B)
- /raw/{id} on a file paste streams the attachment bytes inline with its
  sniffed mime and filename instead of an empty text/plain body

internal/web/web.go

@@ -92,6 +92,25 @@ func humanSize(n int) string {
 	return fmt.Sprintf("%.1f MB", float64(n)/(1024*1024))
 }
 
+// #221: file pastes store their bytes in the blob store with empty text
+// content; the displayed size is the attachment size, not len(Content).
+func pasteDisplaySize(row *store.PasteRow, att *store.Attachment) int64 {
+	if row.Content == "" && att != nil {
+		return att.Size
+	}
+	return int64(len(row.Content))
+}
+
+// attachmentIsImage reports whether a paste-view attachment renders as an
+// image (same set the paste template previews inline, #221).
+func attachmentIsImage(mime string) bool {
+	switch strings.ToLower(strings.TrimSpace(mime)) {
+	case "image/png", "image/jpeg", "image/gif", "image/webp":
+		return true
+	}
+	return false
+}
+
 func (u *UI) StaticHandler() http.Handler {
 	sub, _ := fs.Sub(staticFS, "static")
 	return http.StripPrefix("/static/", http.FileServer(http.FS(sub)))
@@ -245,20 +264,22 @@ func (h *Handlers) renderPaste(w http.ResponseWriter, row *store.PasteRow, justC
 	if lang == "" {
 		lang = "text"
 	}
-	summary := fmt.Sprintf("%s · %s · %d views · %s", lang, humanSize(len(row.Content)), row.ViewCount, agoString(row.CreatedAt))
 	// #38: one optional file attachment per paste; nil when none.
 	attachment, err := h.Store.GetAttachmentForPaste(row.ID)
 	if err != nil {
 		http.Error(w, "db error", 500)
 		return
 	}
+	summary := fmt.Sprintf("%s · %s · %d views · %s", lang, humanSize(int(pasteDisplaySize(row, attachment))), row.ViewCount, agoString(row.CreatedAt))
 	data := map[string]any{
 		"Page":          "paste",
 		"ID":            row.ID,
 		"Title":         row.Title.String,
 		"Language":      row.Language.String,
 		"StatsSummary":  summary,
-		"SizeHuman":     humanSize(len(row.Content)),
+		// #221: file pastes store bytes in the blob store; report the
+		// attachment size, not the (empty) text content length.
+		"SizeHuman":     humanSize(int(pasteDisplaySize(row, attachment))),
 		"HasPassword":   row.PasswordHash.Valid,
 		"BurnAfterRead": row.BurnAfterRead,
 		"CustomSlug":    row.CustomSlug.String,
@@ -279,6 +300,8 @@ func (h *Handlers) renderPaste(w http.ResponseWriter, row *store.PasteRow, justC
 		"ReadsTotal":    int(row.ReadsLimit.Int64),
 		"JustCreated":   justCreated,
 		"Attachment":    attachment,
+		// #221: tells the template to drop the code box for image pastes
+		"AttachmentIsImage": attachment != nil && attachmentIsImage(attachment.Mime),
 		"Host":          "this host",
 	}
 	h.renderPage(w, "paste.html", data)