feat: add device deletion endpoint with cascade cleanup and admin UI integration

Add DELETE /admin/devices/{id} endpoint with cascade deletion of device records, WireGuard peers, IP allocations, and device access profile settings. Update device status to 'deleted' and set deleted_at timestamp while preserving revoked_at if already set.

Add deleteDevice API method and delete button to devices page with query invalidation for both devices and device-profile lists. Record admin.device.deleted audit

admin-web/src/api/client.ts

@@ -225,6 +225,10 @@ export const api = {
       method: "POST",
       body: JSON.stringify({})
     }),
+  deleteDevice: (deviceId: string) =>
+    request<{ ok: boolean }>(`/admin/devices/${deviceId}`, {
+      method: "DELETE"
+    }),
   rotateDevice: (deviceId: string) =>
     request<{ ok: boolean }>(`/admin/devices/${deviceId}/rotate`, {
       method: "POST",