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/example_test.go

@@ -0,0 +1,101 @@
+// Package exporters_test provides examples for the exporters package.
+package exporters_test
+
+import (
+	"fmt"
+	"log"
+
+	"github.com/kjanat/articulate-parser/internal/exporters"
+	"github.com/kjanat/articulate-parser/internal/models"
+	"github.com/kjanat/articulate-parser/internal/services"
+)
+
+// ExampleNewFactory demonstrates creating an exporter factory.
+func ExampleNewFactory() {
+	htmlCleaner := services.NewHTMLCleaner()
+	factory := exporters.NewFactory(htmlCleaner)
+
+	// Get supported formats
+	formats := factory.SupportedFormats()
+	fmt.Printf("Supported formats: %d\n", len(formats))
+	// Output: Supported formats: 6
+}
+
+// ExampleFactory_CreateExporter demonstrates creating exporters.
+func ExampleFactory_CreateExporter() {
+	htmlCleaner := services.NewHTMLCleaner()
+	factory := exporters.NewFactory(htmlCleaner)
+
+	// Create a markdown exporter
+	exporter, err := factory.CreateExporter("markdown")
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	fmt.Printf("Created: %s exporter\n", exporter.SupportedFormat())
+	// Output: Created: markdown exporter
+}
+
+// ExampleFactory_CreateExporter_caseInsensitive demonstrates case-insensitive format names.
+func ExampleFactory_CreateExporter_caseInsensitive() {
+	htmlCleaner := services.NewHTMLCleaner()
+	factory := exporters.NewFactory(htmlCleaner)
+
+	// All these work (case-insensitive)
+	formats := []string{"MARKDOWN", "Markdown", "markdown", "MD"}
+
+	for _, format := range formats {
+		exporter, _ := factory.CreateExporter(format)
+		fmt.Printf("%s -> %s\n", format, exporter.SupportedFormat())
+	}
+	// Output:
+	// MARKDOWN -> markdown
+	// Markdown -> markdown
+	// markdown -> markdown
+	// MD -> markdown
+}
+
+// ExampleMarkdownExporter_Export demonstrates exporting to Markdown.
+func ExampleMarkdownExporter_Export() {
+	htmlCleaner := services.NewHTMLCleaner()
+	exporter := exporters.NewMarkdownExporter(htmlCleaner)
+
+	course := &models.Course{
+		ShareID: "example-id",
+		Course: models.CourseInfo{
+			Title:       "Example Course",
+			Description: "<p>Course description</p>",
+		},
+	}
+
+	// Export to markdown file
+	err := exporter.Export(course, "output.md")
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	fmt.Println("Export complete")
+	// Output: Export complete
+}
+
+// ExampleDocxExporter_Export demonstrates exporting to DOCX.
+func ExampleDocxExporter_Export() {
+	htmlCleaner := services.NewHTMLCleaner()
+	exporter := exporters.NewDocxExporter(htmlCleaner)
+
+	course := &models.Course{
+		ShareID: "example-id",
+		Course: models.CourseInfo{
+			Title: "Example Course",
+		},
+	}
+
+	// Export to Word document
+	err := exporter.Export(course, "output.docx")
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	fmt.Println("DOCX export complete")
+	// Output: DOCX export complete
+}