fix(lint): resolve golangci-lint failures and modernize string handling

CI's golangci-lint (v2.12.2) job was failing with 14 issues, which blocked
the dependent test job. This addresses all of them:

- goconst: extract repeated string literals into constants
  - format aliases ("md", "word", "htm") in the exporter factory
  - "section" lesson type shared by markdown and HTML exporters
  - default Articulate Rise base URL and host in the parser
  - reuse existing itemType* constants in the markdown switch
- staticcheck (QF1012): replace buf.WriteString(fmt.Sprintf(...)) with
  fmt.Fprintf(...) in the markdown exporter

Also drop the hardcoded `go: "1.24"` from .golangci.yml so the target Go
version is autodetected from go.mod.

internal/exporters/factory.go

@@ -13,6 +13,11 @@ const (
 	FormatMarkdown = "markdown"
 	FormatDocx     = "docx"
 	FormatHTML     = "html"
+
+	// Format aliases accepted by CreateExporter.
+	formatAliasMarkdown = "md"
+	formatAliasDocx     = "word"
+	formatAliasHTML     = "htm"
 )
 
 // Factory implements the ExporterFactory interface.
@@ -41,11 +46,11 @@ func NewFactory(htmlCleaner *services.HTMLCleaner) interfaces.ExporterFactory {
 // Format strings are case-insensitive (e.g., "markdown", "DOCX").
 func (f *Factory) CreateExporter(format string) (interfaces.Exporter, error) {
 	switch strings.ToLower(format) {
-	case FormatMarkdown, "md":
+	case FormatMarkdown, formatAliasMarkdown:
 		return NewMarkdownExporter(f.htmlCleaner), nil
-	case FormatDocx, "word":
+	case FormatDocx, formatAliasDocx:
 		return NewDocxExporter(f.htmlCleaner), nil
-	case FormatHTML, "htm":
+	case FormatHTML, formatAliasHTML:
 		return NewHTMLExporter(f.htmlCleaner), nil
 	default:
 		return nil, fmt.Errorf("unsupported export format: %s", format)
@@ -55,5 +60,9 @@ func (f *Factory) CreateExporter(format string) (interfaces.Exporter, error) {
 // SupportedFormats returns a list of all supported export formats,
 // including both primary format names and their aliases.
 func (f *Factory) SupportedFormats() []string {
-	return []string{FormatMarkdown, "md", FormatDocx, "word", FormatHTML, "htm"}
+	return []string{
+		FormatMarkdown, formatAliasMarkdown,
+		FormatDocx, formatAliasDocx,
+		FormatHTML, formatAliasHTML,
+	}
 }

internal/exporters/html_template_data.go

@@ -21,6 +21,9 @@ const (
 	itemTypeDivider        = "divider"
 )
 
+// lessonTypeSection identifies a lesson that acts as a section header.
+const lessonTypeSection = "section"
+
 // templateData represents the data structure passed to the HTML template.
 type templateData struct {
 	Course   models.CourseInfo
@@ -74,7 +77,7 @@ func prepareTemplateData(course *models.Course, htmlCleaner *services.HTMLCleane
 			Description: lesson.Description,
 		}
 
-		if lesson.Type != "section" {
+		if lesson.Type != lessonTypeSection {
 			lessonCounter++
 			section.Number = lessonCounter
 			section.Items = prepareItems(lesson.Items, htmlCleaner)

internal/exporters/markdown.go

@@ -40,35 +40,35 @@ func (e *MarkdownExporter) Export(course *models.Course, outputPath string) erro
 	var buf bytes.Buffer
 
 	// Write course header
-	buf.WriteString(fmt.Sprintf("# %s\n\n", course.Course.Title))
+	fmt.Fprintf(&buf, "# %s\n\n", course.Course.Title)
 
 	if course.Course.Description != "" {
-		buf.WriteString(fmt.Sprintf("%s\n\n", e.htmlCleaner.CleanHTML(course.Course.Description)))
+		fmt.Fprintf(&buf, "%s\n\n", e.htmlCleaner.CleanHTML(course.Course.Description))
 	}
 
 	// Add metadata
 	buf.WriteString("## Course Information\n\n")
-	buf.WriteString(fmt.Sprintf("- **Course ID**: %s\n", course.Course.ID))
-	buf.WriteString(fmt.Sprintf("- **Share ID**: %s\n", course.ShareID))
-	buf.WriteString(fmt.Sprintf("- **Navigation Mode**: %s\n", course.Course.NavigationMode))
+	fmt.Fprintf(&buf, "- **Course ID**: %s\n", course.Course.ID)
+	fmt.Fprintf(&buf, "- **Share ID**: %s\n", course.ShareID)
+	fmt.Fprintf(&buf, "- **Navigation Mode**: %s\n", course.Course.NavigationMode)
 	if course.Course.ExportSettings != nil {
-		buf.WriteString(fmt.Sprintf("- **Export Format**: %s\n", course.Course.ExportSettings.Format))
+		fmt.Fprintf(&buf, "- **Export Format**: %s\n", course.Course.ExportSettings.Format)
 	}
 	buf.WriteString("\n---\n\n")
 
 	// Process lessons
 	lessonCounter := 0
 	for _, lesson := range course.Course.Lessons {
-		if lesson.Type == "section" {
-			buf.WriteString(fmt.Sprintf("# %s\n\n", lesson.Title))
+		if lesson.Type == lessonTypeSection {
+			fmt.Fprintf(&buf, "# %s\n\n", lesson.Title)
 			continue
 		}
 
 		lessonCounter++
-		buf.WriteString(fmt.Sprintf("## Lesson %d: %s\n\n", lessonCounter, lesson.Title))
+		fmt.Fprintf(&buf, "## Lesson %d: %s\n\n", lessonCounter, lesson.Title)
 
 		if lesson.Description != "" {
-			buf.WriteString(fmt.Sprintf("%s\n\n", e.htmlCleaner.CleanHTML(lesson.Description)))
+			fmt.Fprintf(&buf, "%s\n\n", e.htmlCleaner.CleanHTML(lesson.Description))
 		}
 
 		// Process lesson items
@@ -100,19 +100,19 @@ func (e *MarkdownExporter) processItemToMarkdown(buf *bytes.Buffer, item models.
 	itemType := strings.ToLower(item.Type)
 
 	switch itemType {
-	case "text":
+	case itemTypeText:
 		e.processTextItem(buf, item, headingPrefix)
-	case "list":
+	case itemTypeList:
 		e.processListItem(buf, item)
-	case "multimedia":
+	case itemTypeMultimedia:
 		e.processMultimediaItem(buf, item, headingPrefix)
-	case "image":
+	case itemTypeImage:
 		e.processImageItem(buf, item, headingPrefix)
-	case "knowledgecheck":
+	case itemTypeKnowledgeCheck:
 		e.processKnowledgeCheckItem(buf, item, headingPrefix)
-	case "interactive":
+	case itemTypeInteractive:
 		e.processInteractiveItem(buf, item, headingPrefix)
-	case "divider":
+	case itemTypeDivider:
 		e.processDividerItem(buf)
 	default:
 		e.processUnknownItem(buf, item, headingPrefix)