fix prevent fatal from dnh_register_notice()

[f2cmbeapi]

This pull request fixes issue #{id}.

It will apply the following changes :

---

Note

Low Risk
Low risk: adds a simple function_exists guard around an optional admin-notice integration and bumps plugin metadata/version strings.

Overview
Prevents a potential fatal error on admin init by only calling dnh_register_notice() when the function is available.

Bumps the plugin version to 2.1.4 and updates accompanying release metadata (CHANGELOG.md, readme.txt stable tag/tested-up-to).

^{Written by Cursor Bugbot for commit 1c76c2a. This will update automatically on new commits. Configure here.}

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