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

party/registry.go

@@ -6,6 +6,7 @@ import (
 	"sync"
 
 	"git.golem15.com/golem15/summercms/backpack"
+	"git.golem15.com/golem15/summercms/pact"
 )
 
 // Plugin is the required descriptor every compiled plugin implements.
@@ -97,6 +98,13 @@ func activate(registered []Plugin, app *backpack.App, ids []string) ([]Plugin, e
 		return nil, err
 	}
 
+	for _, p := range ordered {
+		if hc, ok := p.(pact.HasConfig); ok && app.Config != nil {
+			if err := app.Config.MergePlugin(p.ID(), hc.ConfigFS()); err != nil {
+				return nil, fmt.Errorf("party: config %s: %w", p.ID(), err)
+			}
+		}
+	}
 	for _, p := range ordered {
 		if err := p.Register(app); err != nil {
 			return nil, fmt.Errorf("party: register %s: %w", p.ID(), err)