Bump better-auth from 1.3.8 to 1.3.29

Bumps [better-auth](https://github.com/better-auth/better-auth/tree/HEAD/packages/better-auth) from 1.3.8 to 1.3.29.
- [Release notes](https://github.com/better-auth/better-auth/releases)
- [Commits](https://github.com/better-auth/better-auth/commits/v1.3.29/packages/better-auth)

---
updated-dependencies:
- dependency-name: better-auth
  dependency-version: 1.3.29
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

packages/backend/package.json

@@ -24,7 +24,7 @@
     "@octokit/types": "^15.0.0",
     "@octokit/webhooks": "^14.1.3",
     "@t3-oss/env-core": "^0.13.8",
-    "better-auth": "1.3.27",
+    "better-auth": "1.3.31",
     "buffer": "^6.0.3",
     "convex": "^1.27.3",
     "convex-helpers": "^0.1.104",