feat(go-config): multi-format codecs, envc CLI, fixtures, ASRs

- Module github.com/eslider/go-config with env/yaml/json/ini packages
- internal: source, keymap, merge, structconv, bytesutil
- cmd/envc: convert, get, merge
- docs/asr ASR-0001..0008, README/CHANGELOG/AGENTS refresh
- golangci-lint v2 config; tests + fixtures

Co-authored-by: Cursor <cursoragent@cursor.com>

env/map_flat_test.go

@@ -0,0 +1,35 @@
+package env
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestNestedFromFlat(t *testing.T) {
+	got := nestedFromFlat(map[string]string{
+		"FOO":               "bar",
+		"SERVICE_HTTP_PORT": "8080",
+		"SERVICE_KEY":       "abc",
+	}, "")
+	want := map[string]any{
+		"foo": "bar",
+		"service": map[string]any{
+			"http": map[string]any{"port": "8080"},
+			"key":  "abc",
+		},
+	}
+	if !reflect.DeepEqual(got, want) {
+		t.Fatalf("got %#v want %#v", got, want)
+	}
+}
+
+func TestNestedFromFlat_FirstWriteWins(t *testing.T) {
+	flat := map[string]string{}
+	flat["A"] = "1"
+	got := nestedFromFlat(flat, "")
+	// Second insert for same key is ignored by insertPath within one build.
+	insertPath(got, []string{"a"}, "2")
+	if got["a"] != "1" {
+		t.Fatalf("got %v", got["a"])
+	}
+}