Updates page is live

AgenTank now has a public update archive in the footer. It gives players a simple place to review past website changes, feature releases, and product adjustments.

What changed:

• Added /updates as the update archive.
• Added /updates/<slug> for individual release notes.
• Added English, Chinese, and Japanese Markdown files for each update.
• Kept update content in the repository under web/updates instead of storing it in the database.

Future updates can be published by adding a new dated folder with localized Markdown files, then pushing the commit to main.