feat: add restart, version, test, backends commands to /ocp plugin

New subcommands:
- /ocp restart [gateway|all] — restart proxy, gateway, or both
- /ocp version — show version, uptime, platform info
- /ocp test — end-to-end proxy test (sends haiku request)
- /ocp backends — list registered backends with health status

Also includes clean-slash-sessions.sh workaround for OpenClaw #26895.

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

clean-slash-sessions.sh

@@ -0,0 +1,10 @@
+#!/bin/bash
+python3 -c "
+import json, glob, os
+for sf in glob.glob(os.path.expanduser('~/.openclaw/agents/*/sessions/sessions.json')):
+    d=json.load(open(sf))
+    keys=[k for k in d if 'slash' in k]
+    if keys:
+        for k in keys: del d[k]
+        json.dump(d, open(sf,'w'), indent=2)
+"