feat(config): app-config registry, env-var renames, wire session.duration from DB

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

backend/cmd/geniusrund/main.go

@@ -35,6 +35,15 @@ func main() {
 	}
 	defer db.Close()
 
+	overrides, err := db.ConfigValues(context.Background())
+	if err != nil {
+		log.Fatalf("app config: %v", err)
+	}
+	appCfg, err := config.LoadApp(overrides)
+	if err != nil {
+		log.Fatalf("app config: %v", err)
+	}
+
 	authVerifier, err := auth.NewOIDCVerifier(context.Background(), auth.OIDCConfig{
 		IssuerURL:    cfg.OIDCIssuerURL,
 		ClientID:     cfg.OIDCClientID,
@@ -49,11 +58,9 @@ func main() {
 	server := api.NewServer(db, garmin.NewClient, garmin.Config{
 		PythonPath:     cfg.GarminPythonPath,
 		TokenStorePath: cfg.GarminTokenStoreRoot,
-	}, appsync.Config{
-		MinConfidence: cfg.MinConfidence,
-	}, authVerifier, api.SessionConfig{
+	}, appsync.Config{}, authVerifier, api.SessionConfig{
 		Secret:      cfg.SessionSecret,
-		Duration:    cfg.SessionDuration,
+		Duration:    appCfg.SessionDuration,
 		Secure:      cfg.SessionSecure,
 		BackendURL:  cfg.BackendURL,
 		FrontendURL: cfg.FrontendURL,