feat: opt-in linked/semantic highlight mode

[TyceHerrman]

Could helpview.nvim provide an opt-in linked/semantic highlight mode where built-in Helpview* groups link to standard Neovim, Tree-sitter, or vimdoc highlight groups instead of generating concrete fg/bg values?

The current dynamic highlight system should remain the default.

The use case is users and colorscheme authors may want colorscheme-owned Helpview colors without copying or predefining a large set of HelpviewPalette* groups. A linked mode would make Helpview decorations inherit from semantic highlight groups directly, so colorschemes can control the final appearance through the groups they already define.

Naming is not important, but something like this could be enough:

require("helpview").setup({
  highlights = {
    style = "linked", -- default could stay "dynamic"
  },
})

or:

require("helpview").setup({
  highlight_style = "linked",
})

Exact mappings tbd, but as an example

HelpviewPalette0Fg = { link = "Comment" },
HelpviewPalette1Fg = { link = "@markup.heading.1.markdown" },
HelpviewPalette2Fg = { link = "@markup.heading.2.markdown" },
HelpviewPalette3Fg = { link = "@markup.heading.3.markdown" },
HelpviewPalette4Fg = { link = "@markup.heading.4.markdown" },
HelpviewPalette5Fg = { link = "@markup.heading.5.markdown" },
HelpviewPalette6Fg = { link = "@markup.heading.6.markdown" },
HelpviewPalette7Fg = { link = "@keyword" },

HelpviewCode = { link = "NormalFloat" },
HelpviewCodeInfo = { link = "Comment" },
HelpviewInlineCode = { link = "@markup.raw" },
HelpviewTaglink = { link = "@markup.link.vimdoc" },
HelpviewOptionlink = { link = "@markup.link.vimdoc" },
HelpviewKeycode = { link = "@string.special.vimdoc" },
HelpviewArgument = { link = "@variable.parameter.vimdoc" },

For groups where Helpview currently computes background variants, linked mode could either link to foreground-only groups or use conservative defaults like NormalFloat, Pmenu, Visual, or CursorLine.

This would let colorschemes integrate with Helpview without duplicating Helpview's generated palette logic. It would also give users a neutral fallback when they prefer their colorscheme to own all plugin UI colors.

[OXY2DEV]

@TyceHerrman, this was the original plan. However, not all colorscheme implement all highlight groups.

And even when they do their colors can vary(e.g. Some colorschemes have background colors for headings while others don't, most colorschemes use separate colors for different diagnostic/warning level but some don't do this).

---

You should still be able to link groups. Just load the colorscheme first(which should be the default) and set the highlight group values inside your colorscheme's config.