chore: Improve code quality and address linter feedback

This commit introduces several improvements across the codebase, primarily focused on enhancing performance, robustness, and developer experience based on static analysis feedback.

- Replaces `WriteString(fmt.Sprintf())` with the more performant `fmt.Fprintf` in the HTML and Markdown exporters.
- Enhances deferred `Close()` operations to log warnings on failure instead of silently ignoring potential I/O issues.
- Explicitly discards non-critical errors in test suites, particularly during file cleanup, to satisfy linters and clarify intent.
- Suppresses command echoing in `Taskfile.yml` for cleaner output during development tasks.

internal/exporters/markdown_test.go

@@ -664,8 +664,10 @@ func BenchmarkMarkdownExporter_Export(b *testing.B) {
 	for b.Loop() {
 		outputPath := filepath.Join(tempDir, "benchmark-course.md")
 		_ = exporter.Export(course, outputPath)
-		// Clean up for next iteration
-		os.Remove(outputPath)
+		// Clean up for next iteration. Remove errors are ignored because we've already
+		// benchmarked the export operation; cleanup failures don't affect the benchmark
+		// measurements or the validity of the next iteration's export.
+		_ = os.Remove(outputPath)
 	}
 }