dispatch: allow empty route kinds (match all) + add routing tests

- config: permit routes[].kinds to be omitted/empty; treat as "all kinds"
- dispatch: compile empty kinds to Route{Kinds:nil} (match all kinds)
- tests: add coverage for route compilation + config validation edge cases

Files:
- config/load.go
- config/config.go
- dispatch/routes.go
- config/validate_test.go
- dispatch/routes_test.go

config/config.go

@@ -54,7 +54,10 @@ type RouteConfig struct {
 	Sink string `yaml:"sink"` // sink name
 
 	// Kinds is domain-defined. feedkit only enforces that each entry is non-empty.
-	// Whether a given daemon "recognizes" a kind is domain-specific validation.
+	//
+	// If Kinds is omitted or empty, the route matches ALL kinds.
+	// This is useful when you want explicit per-sink routing rules even when a
+	// particular sink should receive everything.
 	Kinds []string `yaml:"kinds"`
 }