Stylix discord target needs Vencord-enabled Discord on NixOS

Stylix's discord/vencord target only writes ~/.config/Vencord/themes/stylix.theme.css (with --font-primary etc.). Plain pkgs.discord has no Vencord, so the theme silently never loads and Discord ignores the stylix font. Fix: use (pkgs.discord.override {withVencord = true;}) and enable the theme; pre-seeding ~/.config/Vencord/settings/settings.json with {"enabledThemes":["stylix.theme.css"]} works because Vencord merges defaults. Also: stylix's obsidian target goes through home-manager programs.obsidian, which makes each declared vault's appearance.json a read-only symlink and drops existing cssTheme/snippets unless redeclared; for existing vaults, jq-merging interfaceFontFamily/textFontFamily/monospaceFontFamily is less invasive.