ci: deploy documentation on manual runs

[codeforester]

Summary

Allow the Documentation workflow deployment job to run for both main-branch pushes and explicit workflow dispatches. This closes the final gap found when validating the newly enabled GitHub Pages site.

Issue

Follow-up to #108

Validation

• Reviewed the workflow condition locally.
• The strict documentation build and Pages artifact upload already pass on the merged commit.
• The follow-up allows the post-enable workflow_dispatch run to execute the Pages deployment job.