stylix: full migration off matugen

Flips stylix.autoEnable on so every supported target picks up colours
from the wallpaper-derived base16 palette, and tears out the per-app
matugen plumbing it replaces:

- fred.nix: drop the matugen config.toml block and the .keep files;
  move btop and ghostty to programs.* with the colour-bearing options
  removed (stylix owns those).
- gnome.nix: remove the matugen and jq packages, the hand-written
  gtk.css home.file overrides (replaced by gtk.gtk{3,4}.extraCss layered
  on top of stylix's theme), the WallpaperShell user-themes override,
  and the gtk-theme/cursor-theme/accent-color dconf entries that stylix
  now writes.
- stylix.nix: add a home.activation hook that recolours Adwaita folder
  SVGs using stylix.colors.base0D and pulls in Papirus mimetypes —
  same outcome as the old matugen post-hook but driven by stylix.
- common.nix: drop the matugen invocation from the `update` alias.

Leftover matugen-only behaviour intentionally dropped: Vesktop CSS,
the GNOME accent hue-mapping, the VSCodium colour-merge (stylix's
vscode target handles that natively). Templates in templates/ are kept
on disk for now; can be removed in a follow-up.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

settings/stylix.nix

@@ -8,10 +8,9 @@
       image = "${inputs.self}/walls/wallpaper.png";
       polarity = "dark";
 
-      # Phase 1: opt in to specific targets only. Apps currently handled by
-      # matugen (gtk, ghostty, zen, btop, vscodium, vesktop) keep their
-      # matugen-derived colors — autoEnable would clobber them.
-      autoEnable = false;
+      # Let stylix theme every target it supports. Per-target opt-outs go
+      # under home-manager.users.fred.stylix.targets.<x>.enable = false.
+      autoEnable = true;
 
       cursor = {
         package = pkgs.adwaita-icon-theme;
@@ -24,8 +23,6 @@
           package = pkgs.nerd-fonts.fira-mono;
           name = "FiraMono Nerd Font";
         };
-        # Used by stylix for fuzzel, waybar, mako etc. Stylix defaults this
-        # to DejaVu Sans which looks dated; Inter is a clean modern sans.
         sansSerif = {
           package = pkgs.inter;
           name = "Inter";
@@ -37,14 +34,97 @@
       };
     };
 
-    # Stylix's NixOS module auto-wires homeModules.stylix into every
-    # home-manager user, so we just opt into targets here.
-    home-manager.users.fred.stylix.targets = {
-      waybar.enable = true;
-      fuzzel.enable = true;
-      mako.enable = true;
-      hyprlock.enable = true;
-      hyprland.enable = true;
+    home-manager.users.fred = { config, lib, pkgs, ... }: {
+      # Folder icon recolor — was a matugen post-hook, now driven by
+      # stylix's base16 palette. base0D is the conventional blue/accent
+      # slot, which is what we want for Adwaita-style folder icons.
+      home.activation.recolorFolders = lib.hm.dag.entryAfter [ "writeBoundary" ] ''
+        ICON_DIR="$HOME/.local/share/icons/WallpaperAdwaita"
+        ADWAITA="/run/current-system/sw/share/icons/Adwaita"
+        PAPIRUS="/run/current-system/sw/share/icons/Papirus-Dark"
+        PRIMARY="#${config.lib.stylix.colors.base0D}"
+
+        $DRY_RUN_CMD mkdir -p "$ICON_DIR/scalable/places"
+
+        $DRY_RUN_CMD cat > "$ICON_DIR/index.theme" << 'THEME'
+        [Icon Theme]
+        Name=WallpaperAdwaita
+        Comment=Adwaita with stylix-coloured folders and Papirus mimetypes
+        Inherits=Adwaita,hicolor
+        DisplayDepth=32
+
+        [scalable/places]
+        Size=128
+        MinSize=16
+        MaxSize=512
+        Type=Scalable
+        Context=Places
+
+        [16x16/mimetypes]
+        Size=16
+        Type=Fixed
+        Context=MimeTypes
+
+        [22x22/mimetypes]
+        Size=22
+        Type=Fixed
+        Context=MimeTypes
+
+        [32x32/mimetypes]
+        Size=32
+        Type=Fixed
+        Context=MimeTypes
+
+        [48x48/mimetypes]
+        Size=48
+        Type=Fixed
+        Context=MimeTypes
+
+        [64x64/mimetypes]
+        Size=64
+        MinSize=32
+        MaxSize=128
+        Type=Scalable
+        Context=MimeTypes
+
+        [96x96/mimetypes]
+        Size=96
+        MinSize=64
+        MaxSize=256
+        Type=Scalable
+        Context=MimeTypes
+
+        [128x128/mimetypes]
+        Size=128
+        MinSize=64
+        MaxSize=512
+        Type=Scalable
+        Context=MimeTypes
+        THEME
+
+        if [ -d "$ADWAITA/scalable/places" ]; then
+          for svg in "$ADWAITA/scalable/places"/*.svg; do
+            name=$(basename "$svg")
+            $DRY_RUN_CMD sed \
+              -e "s/#438de6/$PRIMARY/gi" \
+              -e "s/#62a0ea/$PRIMARY/gi" \
+              -e "s/#a4caee/$PRIMARY/gi" \
+              -e "s/#afd4ff/$PRIMARY/gi" \
+              -e "s/#c0d5ea/$PRIMARY/gi" \
+              "$svg" > "$ICON_DIR/scalable/places/$name"
+          done
+        fi
+
+        for size in 16x16 22x22 32x32 48x48 64x64 96x96 128x128; do
+          if [ -d "$PAPIRUS/$size/mimetypes" ]; then
+            $DRY_RUN_CMD rm -rf "$ICON_DIR/$size/mimetypes"
+            $DRY_RUN_CMD mkdir -p "$ICON_DIR/$size/mimetypes"
+            $DRY_RUN_CMD cp -rL "$PAPIRUS/$size/mimetypes"/* "$ICON_DIR/$size/mimetypes/"
+          fi
+        done
+
+        $DRY_RUN_CMD ${pkgs.gtk3}/bin/gtk-update-icon-cache -f "$ICON_DIR" 2>/dev/null || true
+      '';
     };
   };
 }