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>

internal/structconv/structconv_test.go

@@ -0,0 +1,28 @@
+package structconv
+
+import (
+	"fmt"
+	"testing"
+)
+
+func TestDecodeEncodeRoundTrip(t *testing.T) {
+	type nested struct {
+		V int `mapstructure:"v"`
+	}
+	type root struct {
+		A nested `mapstructure:"a"`
+	}
+	in := map[string]any{"a": map[string]any{"v": 7}}
+	var dst root
+	if err := Decode(in, &dst, Options{WeaklyTyped: true, Trim: true}); err != nil {
+		t.Fatal(err)
+	}
+	out, err := Encode(&dst)
+	if err != nil {
+		t.Fatal(err)
+	}
+	am := out["a"].(map[string]any)
+	if fmt.Sprint(am["v"]) != "7" {
+		t.Fatalf("%#v", out)
+	}
+}