#235: rename Language column to Type; attachment pastes show file extension

- history/mine table column 'Language' -> 'Type' (data-sort key 'type')
- /api/public and /api/mine rows gain a 'type' field: file extension for
  attachment pastes, stored language otherwise (default 'text')
- paste page stats label 'Language' -> 'Type'; summary line uses the same
  label; get-paste JSON gains 'type'
- store list queries LEFT JOIN attachments to expose the filename
- table.js sorting accepts the 'type' key

internal/web/web.go

@@ -231,6 +231,20 @@ func (h *Handlers) renderPageStatus(w http.ResponseWriter, name string, status i
 	}
 }
 
+// attachmentExt returns the lowercase file extension (without dot) of a
+// filename, or "" when the name has none. Used by the Type display (#235).
+func attachmentExt(filename string) string {
+	name := filename
+	if i := strings.LastIndexByte(name, '/'); i >= 0 {
+		name = name[i+1:]
+	}
+	i := strings.LastIndexByte(name, '.')
+	if i <= 0 || i == len(name)-1 {
+		return ""
+	}
+	return strings.ToLower(name[i+1:])
+}
+
 func (h *Handlers) renderPaste(w http.ResponseWriter, row *store.PasteRow, justCreated bool, deletionToken string, readsRemaining *int) {
 	lines := strings.Count(row.Content, "\n") + 1
 	gutter := ""
@@ -258,7 +272,17 @@ func (h *Handlers) renderPaste(w http.ResponseWriter, row *store.PasteRow, justC
 	if attachment != nil {
 		summarySize = int(attachment.Size)
 	}
-	summary := fmt.Sprintf("%s · %s · %d views · %s", lang, humanSize(summarySize), row.ViewCount, agoString(row.CreatedAt))
+	// #235: column renamed to "Type". Text pastes keep the detected
+	// language; attachment pastes show the file extension instead.
+	attExt := ""
+	typeLabel := lang
+	if attachment != nil {
+		if ext := attachmentExt(attachment.Filename); ext != "" {
+			attExt = ext
+			typeLabel = ext
+		}
+	}
+	summary := fmt.Sprintf("%s · %s · %d views · %s", typeLabel, humanSize(summarySize), row.ViewCount, agoString(row.CreatedAt))
 	// #221: image attachments render the image, not a text/code box. Size
 	// comes from the attachment's actual file size, not the text content.
 	attImage := false
@@ -278,7 +302,10 @@ func (h *Handlers) renderPaste(w http.ResponseWriter, row *store.PasteRow, justC
 		"Page":          "paste",
 		"ID":            row.ID,
 		"Title":         row.Title.String,
-		"Language":      row.Language.String,
+		"Language":      typeLabel,
+		"TypeLabel":     typeLabel,
+		"HasAttachment":  attachment != nil,
+		"AttachmentExt": attExt,
 		"StatsSummary":  summary,
 		"SizeHuman":     sizeHuman,
 		"HasPassword":   row.PasswordHash.Valid,