favilo/delete buffers

[favilo]

Summary

• Add an Ansible-managed WezTerm role for Debian and Arch, with a reload shortcut, hidden tab bar, and stable window geometry.
• Add Neovim database browsing and completion through vim-dadbod.
• Consolidate Telescope buffer search and deletion under <leader>pb.
• Render Markdown diagrams with Sixel in WezTerm, Kitty graphics in direct Kitty sessions, and an external Mermaid preview when Zellij has no supported graphics backend.
• Add regression coverage for buffer deletion, diagram-backend selection, Mermaid fallback, and diagram redraws.

Testing

• Not run (not requested).