[GHSA] GHSA-ggr8-5vv4-36mx (high) — DeepmergeTS has stack exhaustion when merging recursive object graphs

GHSA-ggr8-5vv4-36mx Severity: high CVE: CVE-2026-40345

DeepmergeTS has stack exhaustion when merging recursive object graphs

### Summary

`deepmerge()` and `deepmergeInto()` can be crashed with a crafted recursive object graph. When both merged values contain self-references at the same property path, the library recurses until Node throws `RangeError: Maximum call stack size exceeded`.

### Det