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/logger_bench_test.go

@@ -0,0 +1,96 @@
+// Package services_test provides benchmarks for the logger implementations.
+package services
+
+import (
+	"context"
+	"io"
+	"log/slog"
+	"testing"
+)
+
+// BenchmarkSlogLogger_Info benchmarks structured JSON logging.
+func BenchmarkSlogLogger_Info(b *testing.B) {
+	// Create logger that writes to io.Discard to avoid benchmark noise
+	opts := &slog.HandlerOptions{Level: slog.LevelInfo}
+	handler := slog.NewJSONHandler(io.Discard, opts)
+	logger := &SlogLogger{logger: slog.New(handler)}
+
+	b.ResetTimer()
+	for b.Loop() {
+		logger.Info("test message", "key1", "value1", "key2", 42, "key3", true)
+	}
+}
+
+// BenchmarkSlogLogger_Debug benchmarks debug level logging.
+func BenchmarkSlogLogger_Debug(b *testing.B) {
+	opts := &slog.HandlerOptions{Level: slog.LevelDebug}
+	handler := slog.NewJSONHandler(io.Discard, opts)
+	logger := &SlogLogger{logger: slog.New(handler)}
+
+	b.ResetTimer()
+	for b.Loop() {
+		logger.Debug("debug message", "operation", "test", "duration", 123)
+	}
+}
+
+// BenchmarkSlogLogger_Error benchmarks error logging.
+func BenchmarkSlogLogger_Error(b *testing.B) {
+	opts := &slog.HandlerOptions{Level: slog.LevelError}
+	handler := slog.NewJSONHandler(io.Discard, opts)
+	logger := &SlogLogger{logger: slog.New(handler)}
+
+	b.ResetTimer()
+	for b.Loop() {
+		logger.Error("error occurred", "error", "test error", "code", 500)
+	}
+}
+
+// BenchmarkTextLogger_Info benchmarks text logging.
+func BenchmarkTextLogger_Info(b *testing.B) {
+	opts := &slog.HandlerOptions{Level: slog.LevelInfo}
+	handler := slog.NewTextHandler(io.Discard, opts)
+	logger := &SlogLogger{logger: slog.New(handler)}
+
+	b.ResetTimer()
+	for b.Loop() {
+		logger.Info("test message", "key1", "value1", "key2", 42)
+	}
+}
+
+// BenchmarkNoOpLogger benchmarks the no-op logger.
+func BenchmarkNoOpLogger(b *testing.B) {
+	logger := NewNoOpLogger()
+
+	b.ResetTimer()
+	for b.Loop() {
+		logger.Info("test message", "key1", "value1", "key2", 42)
+		logger.Error("error message", "error", "test")
+	}
+}
+
+// BenchmarkLogger_With benchmarks logger with context.
+func BenchmarkLogger_With(b *testing.B) {
+	opts := &slog.HandlerOptions{Level: slog.LevelInfo}
+	handler := slog.NewJSONHandler(io.Discard, opts)
+	logger := &SlogLogger{logger: slog.New(handler)}
+
+	b.ResetTimer()
+	for b.Loop() {
+		contextLogger := logger.With("request_id", "123", "user_id", "456")
+		contextLogger.Info("operation completed")
+	}
+}
+
+// BenchmarkLogger_WithContext benchmarks logger with Go context.
+func BenchmarkLogger_WithContext(b *testing.B) {
+	opts := &slog.HandlerOptions{Level: slog.LevelInfo}
+	handler := slog.NewJSONHandler(io.Discard, opts)
+	logger := &SlogLogger{logger: slog.New(handler)}
+	ctx := context.Background()
+
+	b.ResetTimer()
+	for b.Loop() {
+		contextLogger := logger.WithContext(ctx)
+		contextLogger.Info("context operation")
+	}
+}