ci: add workflow_dispatch trigger to mkdocs workflow

Enables manual re-triggering of MKDocs deployments.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: HavenDV

.github/workflows/mkdocs.yml

@@ -1,5 +1,6 @@
 name: MKDocs Deploy
 on:
+  workflow_dispatch:
   push:
     branches:
       - main