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/doc.go

@@ -0,0 +1,14 @@
+// Package env loads dotenv files and process environment variables into nested
+// maps and Go structs. Multiple sources merge with later scalars overriding
+// earlier ones; maps merge recursively.
+//
+// Example:
+//
+//	c := env.New(
+//	    env.WithFile(".default.env"),
+//	    env.WithFile(".env"),
+//	    env.WithCurrentEnvironment(),
+//	)
+//	var cfg MyConfig
+//	if err := c.Unmarshal(&cfg); err != nil { ... }
+package env