feat: add post-generation script to preserve buffer overflow fix

Created scripts/post-generate.sh that automatically re-applies the critical
buffer overflow fix to parser.h after tree-sitter generate runs. This fix
prevents undefined behavior in set_contains() when accessing an empty array.

The script is automatically executed after tree-sitter generate via the npm
generate script. Added generate:only for cases where post-processing should
be skipped.

src/node-types.json

@@ -3307,4 +3307,4 @@
     "type": "~",
     "named": false
   }
-]
+]