fix: commands respect selected environment

Backend: AgentRegistryService gains findByApplicationAndEnvironment()
and environment-aware addGroupCommandWithReplies() overload.
AgentCommandController and ApplicationConfigController accept optional
environment query parameter. When set, commands only target agents in
that environment. Backward compatible — null means all environments.

Frontend: All command mutations (config update, route control, traced
processors, tap config, route recording) now pass selectedEnv to the
backend via query parameter.

Prevents cross-environment command leakage — e.g., updating config for
prod no longer pushes to dev agents.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ui/src/pages/AgentHealth/AgentHealth.tsx

@@ -115,7 +115,7 @@ export default function AgentHealth() {
   const saveConfigEdit = useCallback(() => {
     if (!appConfig) return;
     const updated = { ...appConfig, ...configDraft };
-    updateConfig.mutate(updated, {
+    updateConfig.mutate({ config: updated, environment: selectedEnv }, {
       onSuccess: (saved: ConfigUpdateResponse) => {
         setConfigEditing(false);
         setConfigDraft({});