Fix issue #5363: [Bug]: Slack Invite Link Expired

[openhands-agent]

This pull request fixes #5363.

The issue has been successfully resolved. The AI agent has:

1. Identified all locations where the Slack invite link needed to be updated across the repository
2. Updated the links in all relevant files, including:
   • Main README.md
   • Documentation components (CustomFooter.tsx and HomepageHeader.tsx)
   • Resolver documentation
   • Translated documentation (Chinese and French versions)
3. Confirmed all links now point to the new URL: https://join.slack.com/t/openhands-ai/shared_invite/zt-2vbfigwev-G03twSpXaErwzYVD4CFiBg
4. Correctly noted that no tests were needed as this was purely a documentation update

This PR can be summarized for review as:
"Updated all Slack invite links across the repository to the new URL. Changes span the main README, documentation components, and translated docs. No code changes were required, only documentation updates."

Automatic fix generated by OpenHands 🙌

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To run this PR locally, use the following command:

docker run -it --rm   -p 3000:3000   -v /var/run/docker.sock:/var/run/docker.sock   --add-host host.docker.internal:host-gateway   -e SANDBOX_RUNTIME_CONTAINER_IMAGE=docker.all-hands.dev/all-hands-ai/runtime:0b0a961-nikolaik   --name openhands-app-0b0a961   docker.all-hands.dev/all-hands-ai/openhands:0b0a961