feat: establish Go service and database foundation

internal/config/config_test.go

@@ -0,0 +1,18 @@
+package config
+
+import "testing"
+
+func TestLoadRequiresDatabaseURL(t *testing.T) {
+	t.Setenv("DATABASE_URL", "")
+	if _, err := Load(); err == nil {
+		t.Fatal("Load() error = nil, want required database url error")
+	}
+}
+
+func TestValidateAPIRequiresLongSecret(t *testing.T) {
+	t.Parallel()
+	cfg := Config{SessionSecret: "short"}
+	if err := cfg.ValidateAPI(); err == nil {
+		t.Fatal("ValidateAPI() error = nil, want secret length error")
+	}
+}