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/shared/config/runtime/source.go

@@ -0,0 +1,21 @@
+// Package runtime is adapted from go-kratos/kratos config.
+//
+// Upstream: https://github.com/go-kratos/kratos/tree/v2.9.2/config
+// License: MIT, see LICENSE.kratos in this directory.
+package runtime
+
+type KeyValue struct {
+	Key    string
+	Value  []byte
+	Format string
+}
+
+type Source interface {
+	Load() ([]*KeyValue, error)
+	Watch() (Watcher, error)
+}
+
+type Watcher interface {
+	Next() ([]*KeyValue, error)
+	Stop() error
+}