Reservations page refreshes itself every 15 seconds

Online and last-seen times stay current. A newer draw (typing, a change)
wins over a slower older one; no refresh while the tab is hidden.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

CHANGELOG.md

@@ -113,6 +113,8 @@ and a CLI, built the way Jarl is.
   (Leases page, reservations' online badge, `steward lease list|show`,
   `steward reservation list|show`, `last_seen` in the API). A client that
   blocks pings stays online for as long as its lease lasts, without one.
+- **The Reservations page refreshes itself** every 15 seconds, so online
+  and last seen stay current.
 - **Activity by subnet:** `steward activity --subnet`, a subnet filter on
   the Activity page, `GET /events?subnet=` (ID, name or prefix).
 - **Token rotation** (`steward token rotate`, `POST /tokens/{id}/rotate`,