chore!: upgrade mdex to 0.14

[halostatue]

If a Tableau blog uses MDEx syntax highlighting, the latest two versions of MDEx have breaking changes to how syntax highlighting works and your blog configuration must be modified for it to continue working.

There are two supported syntax highlighters: Lumis (tree-sitter) and Syntect (Sublime Text grammars). This modification to Tableau does not include either syntax highlighter package and shows Syntect as its primary example with a documentation section added for the distinction while linking to the MDEx page for each. Neither syntax highlighter works without modification to the site config/config.exs for selecting the appropriate syntax highlighting NIF:

config :mdex_native, syntax_highlighter: :syntect
config :mdex_native, syntax_highlighter: :lumis

The MDEx options configuration must also be updated:

        render: [unsafe: true],
-       syntax_highlight: [formatter: {:html_inline, theme: "neovim_dark"}],
+       syntax_highlight: [engine: :syntect, theme: "Catppuccin Macchiato"],
        plugins: [MDExGFM]

[halostatue]

@mhanberg This is intended to replace #185; it upgrades to the latest version of MDEx and switches the examples to Syntect because it requires one extra configuration.

Lumis >= 0.9 requires the WASM treesitter bundles added, so that's a lot more.

I've tested this on my site (using the full language bundle for Lumis, since I have languages not supported by Syntect) in dev mode and it looks mostly good except that for some reason that light-dark theme switcher that used to work doesn't and I haven't investigated why, yet.