refactor(logging): move logging setup to internal/logging

Moves logging configuration and setup to a dedicated package. Updates Config struct to use nested LoggingConfig. Updates main.go to use the new logging package.

internal/logging/logging_test.go

@@ -0,0 +1,37 @@
+package logging
+
+import (
+	"log/slog"
+	"testing"
+)
+
+func TestParseLogLevel(t *testing.T) {
+	tests := []struct {
+		input    string
+		expected slog.Level
+	}{
+		{"debug", slog.LevelDebug},
+		{"DEBUG", slog.LevelDebug},
+		{"info", slog.LevelInfo},
+		{"warn", slog.LevelWarn},
+		{"error", slog.LevelError},
+		{"unknown", slog.LevelInfo},
+		{"", slog.LevelInfo},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.input, func(t *testing.T) {
+			if got := parseLogLevel(tt.input); got != tt.expected {
+				t.Errorf("parseLogLevel(%q) = %v, want %v", tt.input, got, tt.expected)
+			}
+		})
+	}
+}
+
+func TestConfigure(t *testing.T) {
+	cfg := Config{Level: "debug"}
+	logger := Configure(cfg)
+	if logger == nil {
+		t.Error("Configure() returned nil")
+	}
+}