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/pages/AgentHealth/AgentHealth.tsx

@@ -63,7 +63,7 @@ function AgentOverviewContent({ agent }: { agent: any }) {
       <dl className={styles.detailList}>
         <div className={styles.detailRow}>
           <dt>Application</dt>
-          <dd><MonoText>{agent.group ?? '—'}</MonoText></dd>
+          <dd><MonoText>{agent.application ?? '—'}</MonoText></dd>
         </div>
         <div className={styles.detailRow}>
           <dt>Version</dt>
@@ -175,7 +175,7 @@ export default function AgentHealth() {
   const agentsByApp = useMemo(() => {
     const map: Record<string, any[]> = {};
     (agents || []).forEach((a: any) => {
-      const g = a.group;
+      const g = a.application;
       if (!map[g]) map[g] = [];
       map[g].push(a);
     });
@@ -185,7 +185,7 @@ export default function AgentHealth() {
   const liveCount = (agents || []).filter((a: any) => a.status === 'LIVE').length;
   const staleCount = (agents || []).filter((a: any) => a.status === 'STALE').length;
   const deadCount = (agents || []).filter((a: any) => a.status === 'DEAD').length;
-  const uniqueApps = new Set((agents || []).map((a: any) => a.group)).size;
+  const uniqueApps = new Set((agents || []).map((a: any) => a.application)).size;
   const activeRoutes = (agents || []).filter((a: any) => a.status === 'LIVE').reduce((sum: number, a: any) => sum + (a.activeRoutes || 0), 0);
   const totalTps = (agents || []).filter((a: any) => a.status === 'LIVE').reduce((sum: number, a: any) => sum + (a.tps || 0), 0);