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>

example_hero_test.go

@@ -0,0 +1,20 @@
+package config_test
+
+import (
+	"fmt"
+
+	"github.com/eslider/go-config/env"
+	"github.com/eslider/go-config/yaml"
+)
+
+func Example_hero_offline() {
+	// README hero pattern using offline sources (no network, no .env files).
+	y := yaml.New(yaml.WithBytes([]byte(`service: { name: demo }`)))
+	e := env.New(env.WithBytes([]byte("SERVICE_PORT=8080")))
+	var m map[string]any
+	_ = y.Unmarshal(&m)
+	var flat map[string]any
+	_ = e.Unmarshal(&flat)
+	fmt.Println(m["service"].(map[string]any)["name"], flat["service"].(map[string]any)["port"])
+	// Output: demo 8080
+}