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/services/example_test.go

@@ -0,0 +1,96 @@
+// Package services_test provides examples for the services package.
+package services_test
+
+import (
+	"context"
+	"fmt"
+	"log"
+
+	"github.com/kjanat/articulate-parser/internal/services"
+)
+
+// ExampleNewArticulateParser demonstrates creating a new parser.
+func ExampleNewArticulateParser() {
+	// Create a no-op logger for this example
+	logger := services.NewNoOpLogger()
+
+	// Create parser with defaults
+	parser := services.NewArticulateParser(logger, "", 0)
+
+	fmt.Printf("Parser created: %T\n", parser)
+	// Output: Parser created: *services.ArticulateParser
+}
+
+// ExampleNewArticulateParser_custom demonstrates creating a parser with custom configuration.
+func ExampleNewArticulateParser_custom() {
+	logger := services.NewNoOpLogger()
+
+	// Create parser with custom base URL and timeout
+	parser := services.NewArticulateParser(
+		logger,
+		"https://custom.articulate.com",
+		60_000_000_000, // 60 seconds in nanoseconds
+	)
+
+	fmt.Printf("Parser configured: %T\n", parser)
+	// Output: Parser configured: *services.ArticulateParser
+}
+
+// ExampleArticulateParser_LoadCourseFromFile demonstrates loading a course from a file.
+func ExampleArticulateParser_LoadCourseFromFile() {
+	logger := services.NewNoOpLogger()
+	parser := services.NewArticulateParser(logger, "", 0)
+
+	// In a real scenario, you'd have an actual file
+	// This example shows the API usage
+	_, err := parser.LoadCourseFromFile("course.json")
+	if err != nil {
+		log.Printf("Failed to load course: %v", err)
+	}
+}
+
+// ExampleArticulateParser_FetchCourse demonstrates fetching a course from a URI.
+func ExampleArticulateParser_FetchCourse() {
+	logger := services.NewNoOpLogger()
+	parser := services.NewArticulateParser(logger, "", 0)
+
+	// Create a context with timeout
+	ctx := context.Background()
+
+	// In a real scenario, you'd use an actual share URL
+	_, err := parser.FetchCourse(ctx, "https://rise.articulate.com/share/YOUR_SHARE_ID")
+	if err != nil {
+		log.Printf("Failed to fetch course: %v", err)
+	}
+}
+
+// ExampleHTMLCleaner demonstrates cleaning HTML content.
+func ExampleHTMLCleaner() {
+	cleaner := services.NewHTMLCleaner()
+
+	html := "<p>This is <strong>bold</strong> text with entities.</p>"
+	clean := cleaner.CleanHTML(html)
+
+	fmt.Println(clean)
+	// Output: This is bold text with entities.
+}
+
+// ExampleHTMLCleaner_CleanHTML demonstrates complex HTML cleaning.
+func ExampleHTMLCleaner_CleanHTML() {
+	cleaner := services.NewHTMLCleaner()
+
+	html := `
+		<div>
+			<h1>Title</h1>
+			<p>Paragraph with <a href="#">link</a> and &amp; entity.</p>
+			<ul>
+				<li>Item 1</li>
+				<li>Item 2</li>
+			</ul>
+		</div>
+	`
+	clean := cleaner.CleanHTML(html)
+
+	fmt.Println(clean)
+	// Output: Title Paragraph with link and & entity. Item 1 Item 2
+}