Fix guifont escaping

[igorgladkoborodov]

Summary

Neovim 0.12 silently overrode VVset fontfamily=... from init.vim. The font stuck on SF Mono. The same command worked when typed after startup. It ships &guifont defaulting to SF Mono,Menlo,Monaco,Courier New,monospace and emits it via option_set at UI attach. The renderer's optionSet.guifont handler echoed it back as :VVset fontfamily=..., overwriting the user's value.

Neovim 0.11 had an empty default &guifont, so the loop never ran.

Fix

Drop the renderer-side guifont → VVset feedback and move the sync into vvset.vim. Now VVset and &guifont track each other in both directions, with a guard against recursion.

Test plan

• VVset fontfamily=Menlo in init.vim, no set guifont=. Font applies on first paint. :set guifont? reads Menlo.
• :set guifont=Monaco:h10 updates both family and size.