refactor: rename agent group→application across entire codebase

Complete the group→application terminology rename in the agent
registry subsystem:

- AgentInfo: field group → application, all wither methods updated
- AgentRegistryService: findByGroup → findByApplication
- AgentInstanceResponse: field group → application (API response)
- AgentRegistrationRequest: field group → application (API request)
- JwtServiceImpl: parameter names group → application (JWT claim
  string "group" preserved for token backward compatibility)
- All controllers, lifecycle monitor, command controller updated
- Integration tests: JSON request bodies "group" → "application"
- Frontend: schema.d.ts, openapi.json, agent queries, AgentHealth

RBAC group references (groups table, GroupAdminController, etc.)
are NOT affected — they are a separate domain concept.

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

ui/src/api/queries/agents.ts

@@ -3,12 +3,12 @@ import { api } from '../client';
 import { config } from '../../config';
 import { useAuthStore } from '../../auth/auth-store';
 
-export function useAgents(status?: string, group?: string) {
+export function useAgents(status?: string, application?: string) {
   return useQuery({
-    queryKey: ['agents', status, group],
+    queryKey: ['agents', status, application],
     queryFn: async () => {
       const { data, error } = await api.GET('/agents', {
-        params: { query: { ...(status ? { status } : {}), ...(group ? { group } : {}) } },
+        params: { query: { ...(status ? { status } : {}), ...(application ? { application } : {}) } },
       });
       if (error) throw new Error('Failed to load agents');
       return data!;