What's Changed

• Harden the link-unfurl guard against SSRF via IPv6 transition ranges (NAT64, 6to4)
  and CGNAT, so link previews can't be steered to internal addresses (#225).
  A security advisory with a CVE will follow.
• Upgrade loofah to 2.25.2 and rails-html-sanitizer to 1.7.1 (#221)
• Bump sqlite3 to 2.9.5 (#222)
• Bump websocket-driver to 0.8.2
• Add a development guide and backup/restore instructions
• Improve self-hosting instructions, explain Docker image tagging, and recommend
  the latest tag over main