Fix readline buffer limit (10MB) and evaluator spec filename

- ocaml_bridge: 10MB readline buffer for large spec explorer responses
- nav-data: evaluator.sx filename (was eval.sx, actual spec file is evaluator.sx)

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

shared/sx/ocaml_bridge.py

@@ -62,6 +62,7 @@ class OcamlBridge:
             stdin=asyncio.subprocess.PIPE,
             stdout=asyncio.subprocess.PIPE,
             stderr=asyncio.subprocess.PIPE,
+            limit=10 * 1024 * 1024,  # 10MB readline buffer for large spec data
         )
 
         # Wait for (ready)