chore(core): Add typescript/unified-signatures rule to oxlint config

This rule was available in oxlint but missed during the ESLint migration.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: antonis

packages/core/.oxlintrc.json

@@ -55,6 +55,7 @@
         "typescript/explicit-function-return-type": ["error", { "allowExpressions": true }],
         "typescript/no-floating-promises": ["error", { "ignoreVoid": false }],
         "typescript/no-dynamic-delete": "error",
+        "typescript/unified-signatures": "error",
         "typescript/no-unsafe-member-access": "error",
         "typescript/unbound-method": "error",
         "typescript/no-explicit-any": "warn",