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/internal/tenant/transport/router.go

@@ -247,7 +247,7 @@ func RegisterRoutes(app *bootstrap.App) {
 	imageFolders.GET("/:id/delete-preview", imgHandler.FolderDeletePreview)
 	imageFolders.DELETE("/:id", imgHandler.DeleteFolder)
 
-	if swagger.EnabledForMode(app.Config.Server.Mode) {
+	if swagger.EnabledForMode(app.Config().Server.Mode) {
 		swagger.Register(app.Engine, swagger.Config{
 			Title:   "省心推 Admin API",
 			Version: "dev",