#13874: docs: add Zeabur deployment guide for OpenClaw

Summary - Add a Zeabur deployment guide (docs/install/zeabur.md) covering one-click deploy, resource requirements, first login, data persistence, backup/restore, and troubleshooting. Deploy OpenClaw on Zeabur with one click — just pick a domain and a dedicated server. The guide covers resource requirements (minimum 2 vCPU / 4 GB), first login via the Web UI link, data persistence, backup/restore, and common troubleshooting steps. Test plan - Verify the doc renders correctly in the docs site - Confirm all links (template button, Zeabur docs) are valid 🤖 Generated with https://claude.com/claude-code <!-- greptile_comment --> <h2>Greptile Overview</h2> <h3>Greptile Summary</h3> Added comprehensive deployment guide for Zeabur platform covering one-click deployment, resource requirements, first login via Web UI, Telegram/WhatsApp channel configuration, data persistence under `/home/node`, backup/restore procedures, and troubleshooting for common issues. The guide follows the established pattern from Railway and Northflank deployment docs and integrates properly into the documentation structure. <h3>Confidence Score: 5/5</h3> - This PR is safe to merge with no concerns - This is a documentation-only PR that adds a new deployment guide. The changes are well-structured, follow existing patterns from Railway and Northflank guides, correctly update the docs.json navigation structure, and include appropriate linking. No code changes, no security concerns, and the documentation style is consistent with the project conventions. - No files require special attention <!-- greptile_other_comments_section --> _{(4/5) You can add custom instructions or style guidelines for the agent [here](https://app.greptile.com/review/github)!} <!-- /greptile_comment -->