cockpit: fix bridge EMFILE — batch status reads into one spawn, raise fd limit

The Python cockpit-bridge frees spawn-pipe fds only at GC time; the Van
Router page's ~12 cockpit.spawn calls every 5s saw-toothed the bridge to
its 1024-fd soft limit, so the polkit admin-escalation spawn failed with
"Too many files open" whenever it landed near a peak.

Two-sided fix:
- vanrouter.js gathers all read-only status in ONE `sh -c` spawn per
  refresh, sections delimited by @@vr:<name>@@ marker lines (~12x less
  pipe churn). Mutating actions unchanged.
- cockpit-session@.service drop-in raises LimitNOFILE to 65535
  (hard limit is 524288), installed by deploy.sh.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

cockpit/cockpit-session-nofile.conf

@@ -0,0 +1,5 @@
+# cockpit-session@.service drop-in: the Python cockpit-bridge frees spawn-pipe
+# fds only at GC time; the stock 1024 soft limit is too tight for a polling
+# dashboard and EMFILEs the polkit/sudo escalation spawn. Hard limit is 524288.
+[Service]
+LimitNOFILE=65535