Zag binding tests fail with missing Gea runtime symbols

## Summary

The gea-ui Zag binding regression tests fail on current `main` before they reach the component behavior being tested.

## Reproduction

Run:

```bash
npx tsx --test packages/gea-ui/tests/zag-bindings.test.ts
```

## Actual Result

The tests fail during the manual source evaluation step. The first baseline failure is:

```text
ReferenceError: GEA_UPDATE_PROPS is not defined
```

After providing that symbol, the same loader pattern also exposes missing compiler/runtime bindings such as:

```text
ReferenceError: GEA_ON_PROP_CHANGE is not defined
```

## Expected Result

The test harness should provide the local Gea runtime/compiler bindings needed by transformed component sources, so the tests can execute the real Zag-backed components.

## Notes

The tests read component sources, strip import statements, and execute the transformed code with `new Function(...)`.

Gea now uses symbol-based runtime internals exported from local core source files, but the test loader still injects only the older limited binding set. This makes the tests fail on `main` even before any DatePicker-specific changes are involved.