feat(01-02): implement layered compass config

- Merge plugin defaults, sorted YAML, SUMMER_ env, overrides and Set
- Persist atomically to env overrides; Reload clears runtime Set
- Discover HasConfig before Register and print layered hello values

go.mod

@@ -6,11 +6,15 @@ toolchain go1.27.0
 
 require (
 	github.com/knadh/koanf/parsers/yaml v1.1.1
+	github.com/knadh/koanf/providers/confmap v1.0.1
+	github.com/knadh/koanf/providers/env/v2 v2.0.1
+	github.com/knadh/koanf/providers/file v1.2.1
 	github.com/knadh/koanf/v2 v2.3.6
 	github.com/spf13/cobra v1.10.2
 )
 
 require (
+	github.com/fsnotify/fsnotify v1.9.0 // indirect
 	github.com/go-viper/mapstructure/v2 v2.4.0 // indirect
 	github.com/inconshreveable/mousetrap v1.1.0 // indirect
 	github.com/knadh/koanf/maps v0.1.2 // indirect
@@ -18,4 +22,5 @@ require (
 	github.com/mitchellh/reflectwalk v1.0.2 // indirect
 	github.com/spf13/pflag v1.0.9 // indirect
 	go.yaml.in/yaml/v3 v3.0.4 // indirect
+	golang.org/x/sys v0.32.0 // indirect
 )