refactor(core)!: Add context, config, and structured logging

Introduces `context.Context` to the `FetchCourse` method and its call chain, allowing for cancellable network requests and timeouts. This improves application robustness when fetching remote course data.

A new configuration package centralizes application settings, loading them from environment variables with sensible defaults for base URL, request timeout, and logging.

Standard `log` and `fmt` calls are replaced with a structured logging system built on `slog`, supporting both JSON and human-readable text formats.

This change also includes:
- Extensive benchmarks and example tests.
- Simplified Go doc comments across several packages.

BREAKING CHANGE: The `NewArticulateParser` constructor signature has been updated to accept a logger, base URL, and timeout, which are now supplied via the new configuration system.

internal/exporters/bench_test.go

@@ -0,0 +1,201 @@
+// Package exporters_test provides benchmarks for all exporters.
+package exporters
+
+import (
+	"path/filepath"
+	"testing"
+
+	"github.com/kjanat/articulate-parser/internal/models"
+	"github.com/kjanat/articulate-parser/internal/services"
+)
+
+// BenchmarkFactory_CreateExporter_Markdown benchmarks markdown exporter creation.
+func BenchmarkFactory_CreateExporter_Markdown(b *testing.B) {
+	htmlCleaner := services.NewHTMLCleaner()
+	factory := NewFactory(htmlCleaner)
+
+	b.ResetTimer()
+	for b.Loop() {
+		_, _ = factory.CreateExporter("markdown")
+	}
+}
+
+// BenchmarkFactory_CreateExporter_All benchmarks creating all exporter types.
+func BenchmarkFactory_CreateExporter_All(b *testing.B) {
+	htmlCleaner := services.NewHTMLCleaner()
+	factory := NewFactory(htmlCleaner)
+	formats := []string{"markdown", "docx", "html"}
+
+	b.ResetTimer()
+	for b.Loop() {
+		for _, format := range formats {
+			_, _ = factory.CreateExporter(format)
+		}
+	}
+}
+
+// BenchmarkAllExporters_Export benchmarks all exporters with the same course.
+func BenchmarkAllExporters_Export(b *testing.B) {
+	htmlCleaner := services.NewHTMLCleaner()
+	course := createBenchmarkCourse()
+
+	exporters := map[string]struct {
+		exporter any
+		ext      string
+	}{
+		"Markdown": {NewMarkdownExporter(htmlCleaner), ".md"},
+		"Docx":     {NewDocxExporter(htmlCleaner), ".docx"},
+		"HTML":     {NewHTMLExporter(htmlCleaner), ".html"},
+	}
+
+	for name, exp := range exporters {
+		b.Run(name, func(b *testing.B) {
+			tempDir := b.TempDir()
+			exporter := exp.exporter.(interface {
+				Export(*models.Course, string) error
+			})
+
+			b.ResetTimer()
+			for b.Loop() {
+				outputPath := filepath.Join(tempDir, "benchmark"+exp.ext)
+				_ = exporter.Export(course, outputPath)
+			}
+		})
+	}
+}
+
+// BenchmarkExporters_LargeCourse benchmarks exporters with large course data.
+func BenchmarkExporters_LargeCourse(b *testing.B) {
+	htmlCleaner := services.NewHTMLCleaner()
+	course := createLargeBenchmarkCourse()
+
+	b.Run("Markdown_Large", func(b *testing.B) {
+		exporter := NewMarkdownExporter(htmlCleaner)
+		tempDir := b.TempDir()
+
+		b.ResetTimer()
+		for b.Loop() {
+			outputPath := filepath.Join(tempDir, "large.md")
+			_ = exporter.Export(course, outputPath)
+		}
+	})
+
+	b.Run("Docx_Large", func(b *testing.B) {
+		exporter := NewDocxExporter(htmlCleaner)
+		tempDir := b.TempDir()
+
+		b.ResetTimer()
+		for b.Loop() {
+			outputPath := filepath.Join(tempDir, "large.docx")
+			_ = exporter.Export(course, outputPath)
+		}
+	})
+
+	b.Run("HTML_Large", func(b *testing.B) {
+		exporter := NewHTMLExporter(htmlCleaner)
+		tempDir := b.TempDir()
+
+		b.ResetTimer()
+		for b.Loop() {
+			outputPath := filepath.Join(tempDir, "large.html")
+			_ = exporter.Export(course, outputPath)
+		}
+	})
+}
+
+// createBenchmarkCourse creates a standard-sized course for benchmarking.
+func createBenchmarkCourse() *models.Course {
+	return &models.Course{
+		ShareID: "benchmark-id",
+		Author:  "Benchmark Author",
+		Course: models.CourseInfo{
+			ID:             "bench-course",
+			Title:          "Benchmark Course",
+			Description:    "Performance testing course",
+			NavigationMode: "menu",
+			Lessons: []models.Lesson{
+				{
+					ID:    "lesson1",
+					Title: "Introduction",
+					Type:  "lesson",
+					Items: []models.Item{
+						{
+							Type: "text",
+							Items: []models.SubItem{
+								{
+									Heading:   "Welcome",
+									Paragraph: "<p>This is a test paragraph with <strong>HTML</strong> content.</p>",
+								},
+							},
+						},
+						{
+							Type: "list",
+							Items: []models.SubItem{
+								{Paragraph: "Item 1"},
+								{Paragraph: "Item 2"},
+								{Paragraph: "Item 3"},
+							},
+						},
+					},
+				},
+			},
+		},
+	}
+}
+
+// createLargeBenchmarkCourse creates a large course for stress testing.
+func createLargeBenchmarkCourse() *models.Course {
+	lessons := make([]models.Lesson, 50)
+	for i := 0; i < 50; i++ {
+		lessons[i] = models.Lesson{
+			ID:          string(rune(i)),
+			Title:       "Lesson " + string(rune(i)),
+			Type:        "lesson",
+			Description: "<p>This is lesson description with <em>formatting</em>.</p>",
+			Items: []models.Item{
+				{
+					Type: "text",
+					Items: []models.SubItem{
+						{
+							Heading:   "Section Heading",
+							Paragraph: "<p>Content with <strong>bold</strong> and <em>italic</em> text.</p>",
+						},
+					},
+				},
+				{
+					Type: "list",
+					Items: []models.SubItem{
+						{Paragraph: "Point 1"},
+						{Paragraph: "Point 2"},
+						{Paragraph: "Point 3"},
+					},
+				},
+				{
+					Type: "knowledgeCheck",
+					Items: []models.SubItem{
+						{
+							Title: "Quiz Question",
+							Answers: []models.Answer{
+								{Title: "Answer A", Correct: false},
+								{Title: "Answer B", Correct: true},
+								{Title: "Answer C", Correct: false},
+							},
+							Feedback: "Good job!",
+						},
+					},
+				},
+			},
+		}
+	}
+
+	return &models.Course{
+		ShareID: "large-benchmark-id",
+		Author:  "Benchmark Author",
+		Course: models.CourseInfo{
+			ID:          "large-bench-course",
+			Title:       "Large Benchmark Course",
+			Description: "Large performance testing course",
+			Lessons:     lessons,
+		},
+	}
+}