docs: node relaxation in features, MCP guide, control protocol, literature and the meshing skill (#398)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UhhZMBTviDQxZvwnyP89fo

crates/engine/src/cmd/forms.rs

@@ -1891,6 +1891,7 @@ mod tests {
         "has a result",
         "no crash report",
         "FIELDCRAFT_CRASH_TEST",
+        "no relaxation field",
     ];
 
     /// Fill top-level required names (a fresh one) and references (the first existing item).