chore(deps)(deps): bump @ax-llm/ax from 16.1.12 to 19.0.16

Bumps [@ax-llm/ax](https://github.com/ax-llm/ax) from 16.1.12 to 19.0.16.
- [Release notes](https://github.com/ax-llm/ax/releases)
- [Changelog](https://github.com/ax-llm/ax/blob/main/CHANGELOG.md)
- [Commits](ax-llm/ax@16.1.12...19.0.16)

---
updated-dependencies:
- dependency-name: "@ax-llm/ax"
  dependency-version: 19.0.16
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

packages/ax-signatures/package.json

@@ -12,6 +12,6 @@
     "test": "bun test"
   },
   "dependencies": {
-    "@ax-llm/ax": "^16.0.10"
+    "@ax-llm/ax": "^19.0.16"
   }
 }