ci(docs): only trigger docs workflow on docs-related changes

[dr4gon123]

Summary

• Added paths filters to the push and pull_request triggers in docs.yml
• Workflow now only runs when docs/**, mkdocs.yml, requirements.txt, or the workflow file itself changes
• workflow_dispatch kept for manual triggering

Test plan

• Verify a non-docs commit does not trigger the workflow
• Verify a change under docs/ or mkdocs.yml does trigger the workflow
• Verify manual dispatch still works

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