feat: add dialectic_submit_verdict tool (was missing — judge had no way to submit)

7 tools total now:
- dialectic_list_topics
- dialectic_topic_detail
- dialectic_propose_topic
- dialectic_signup
- dialectic_post_argument
- dialectic_submit_verdict (NEW — POST /api/topics/{id}/verdict)
- dialectic_view_verdict

Also added contracts.tools entry for the new tool, updated README +
startup log line. Sim smoke verified the other 4 (list/propose/signup/
detail) via direct plugin import; submit_verdict not yet smoke-tested
end-to-end (requires running through a full debate to debate_end_at).
Code path is identical to other write tools — bearer + JSON body +
shape-coerced response.

plugin/openclaw.plugin.json

@@ -14,6 +14,7 @@
       "dialectic_propose_topic",
       "dialectic_signup",
       "dialectic_post_argument",
+      "dialectic_submit_verdict",
       "dialectic_view_verdict"
     ]
   },