feat(server): hot-reload config store and reloadable infra clients

- Replace single Load() with a watching Store that re-reads config files
  (and config.local.yaml) and fans out a ReloadEvent with a per-field diff
  so consumers can decide whether the change is hot-applicable or requires
  a process restart.
- Wrap llm, retrieval, vector store, and object storage clients in
  Reloadable* shells so the bootstrap can swap their underlying impls when
  config changes without re-instantiating handlers.
- Make jwt.Manager and ops TokenIssuer mutable under a lock so secrets and
  TTLs can be rotated live; thread default plan code through a setter on
  the ops AdminUserService.
- Wire ConfigStore through bootstrap and every cmd/main.go, scheduler /
  worker / tenant-api / ops-api start the watcher; services and handlers
  take a config.Provider so they always read current values for things
  like generation.stream_enabled, scheduler dispatch, retrieval, etc.
- Switch shared/config decoding off viper to a Kratos-derived runtime
  package so env placeholders (\${VAR:default}) resolve consistently and
  the same source machinery powers both the loader and the watcher.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

server/cmd/kol-assist-worker/main.go

@@ -26,6 +26,8 @@ func main() {
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()
 
+	app.StartConfigWatcher(ctx)
+
 	assistworker.NewKolAssistWorker(
 		app.DB,
 		app.RabbitMQ,
@@ -33,9 +35,9 @@ func main() {
 		app.LLM,
 		app.Logger,
 		app.Cache,
-		app.Config.Generation.WorkerConcurrency,
-		app.Config.Generation.ArticleTimeout,
-	).Start(ctx)
+		app.Config().Generation.WorkerConcurrency,
+		app.Config().Generation.ArticleTimeout,
+	).WithConfigProvider(app.ConfigStore).Start(ctx)
 
 	app.Logger.Info("kol-assist-worker started")