webui 删除彻底化：清理残留 config/defs/provider 悬空

审计发现 webui 多处删除只清一处、留下鬼影：
- RemovePlugin: 仅 DROP config_<name> 与 defs，config 表 plugin.<name>.* 键永不删 →
  补 DELETE config LIKE 'plugin.<name>.%'
- ConfigRegistry.Delete: 删 core.llm.sources.<name>.* 后遗留 ConfigDef、且删 core.llm.*
  不更新 guard 快照（重启/failback 会把已删源复活）→ 同步清 source defs + 写 llm 快照
- llm_impl.ReloadFromConfig: 删除默认源后 core.llm.provider 悬空，SetDefault 指向不存在源
  → 仅当源仍注册时才 SetDefault
- clawhubadapter 测试 mockSettings 补 RemoveCore/RemovePlugin
- mcp 服务器删除仍为进程内需 reload 生效（符合既有 removeServerHandler 语义）

验证: go test ./... 26 包 0 失败；本机部署 sources=3、27 插件加载、对话正常

internal/config/registry.go

@@ -91,6 +91,9 @@ func (r *ConfigRegistry) RemovePlugin(name string) error {
 			delete(r.defs, k)
 		}
 	}
+	if _, err := r.db.Exec(`DELETE FROM config WHERE key LIKE ?`, prefix+"%"); err != nil {
+		return err
+	}
 	table := r.pluginTableName(name)
 	_, err := r.db.Exec(fmt.Sprintf(`DROP TABLE IF EXISTS %s`, table))
 	return err
@@ -307,6 +310,23 @@ func (r *ConfigRegistry) Delete(key string) error {
 	r.mu.Lock()
 	defer r.mu.Unlock()
 	_, err := r.db.Exec(`DELETE FROM config WHERE key = ?`, key)
+	if err == nil {
+		if strings.HasPrefix(key, "core.llm.sources.") {
+			rest := strings.TrimPrefix(key, "core.llm.sources.")
+			parts := strings.SplitN(rest, ".", 2)
+			if len(parts) == 2 {
+				prefix := "core.llm.sources." + parts[0] + "."
+				for k := range r.defs {
+					if strings.HasPrefix(k, prefix) {
+						delete(r.defs, k)
+					}
+				}
+			}
+		}
+		if strings.HasPrefix(key, "core.llm.") {
+			r.writeLLMSnapshotLocked()
+		}
+	}
 	return err
 }