fix(mcp): classify judge_lesson_link as a write tool (#4630)

The tool-classification guard (test_mcp_auth) failed CI run 705: the new
judge_lesson_link tool sat in no set, so a read key would have been silently
denied it. It changes a link's state, so it belongs in _WRITE_TOOLS.

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

src/scribe/mcp/server.py

@@ -161,7 +161,7 @@ _READ_ONLY_TOOLS = frozenset({
 _WRITE_TOOLS = frozenset({
     # notes, tasks, planning
     "create_note", "update_note", "delete_note",
-    "create_lesson", "update_lesson", "delete_lesson",
+    "create_lesson", "update_lesson", "delete_lesson", "judge_lesson_link",
     "create_task", "update_task", "delete_task", "add_task_log",
     "create_records", "start_planning",
     "create_milestone", "update_milestone", "delete_milestone",