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

doc.go

@@ -234,7 +234,8 @@
 //   - dispatch.Fanout: one buffered queue + worker goroutine per sink
 //
 //   - dispatch.CompileRoutes(*config.Config) compiles cfg.Routes into []dispatch.Route.
-//     If routes: is omitted, it defaults to "all sinks receive all kinds".
+//     If routes: is omitted, it defaults to "all sinks receive all kinds". If a route
+//     omits kinds: (or sets it empty), that route matches all kinds.
 //
 //   - logging
 //     Shared logger type used across feedkit packages.