fix: use short config keys in RegisterDef, remove generics helpers

- qq, a2a, bili, files, rss: RegisterDef keys changed from
  namespaced (e.g. "plugin.qq.listen") to short flat keys ("listen")
- a2a, bili: Get() calls updated to match short keys
- rss: replaced readCfg generics with getSetting, added SetAutoRestart(true)
- files: already uses short key Get, only RegisterDef needed fixing

example/files/plugin.go

@@ -25,7 +25,7 @@ func (p *Plugin) Start(s *sdk.PluginSDK) error {
 	s.SetAutoRestart(true)
 	p.sdk = s
 	s.Settings().RegisterDef(sdk.ConfigDef{
-		Key:         "plugin.files.dir",
+		Key:         "dir",
 		Default:     "/",
 		Type:        "string",
 		DisplayName: "文件系统根目录",