feat: Deploy docs only when package is published with a new tag

[other-yuka]

Changes

• Added a Vercel deploy workflow that only updates docs when we create a new tag
• Turned off Vercel's automatic Git deploys so only our GitHub Actions workflow can update the docs
• Now docs update at the same time as the package is published

Background

Before, docs would update whenever we merged code to the main branch. this was a problem because people could see the new docs before the package was actually available to use. This change makes sure docs and the package update together.

How to Test

I've already verified this functionality in my personal repository:

1. Push to main branch: deploy-docs was skipped as expected
   https://github.com/other-yuka/es-git/actions/runs/14342063510
2. Push a new tag: deploy-docs workflow executed successfully
   https://github.com/other-yuka/es-git/actions/runs/14342126756

Important Setup Required

for this workflow to run properly, the following secret keys must be added to the repository:

• VERCEL_ORG_ID
• VERCEL_PROJECT_ID
• VERCEL_TOKEN

Closes #90

[seokju-na]

Added secret to github actions. Thanks a lot!