feat(desktop): viewers (zathura+imv) + xdg-mime defaults (item 8)

The complete-workstation gap: no PDF/image viewer shipped and nothing
set mime defaults, so 'open a photo' fell to GIMP. Two new default-on
toggles: nomarchy.viewers (programs.zathura — Stylix themes it, target
added to the explicit list — plus imv) and nomarchy.mime (mkDefault
xdg.mimeApps: pdf→zathura, image→imv, av→mpv, text→code, dir→thunar;
html/http(s)→firefox as inert entries that only activate when a
browser is installed — the ship-a-browser Decision stays open, now
smaller). Associations for absent apps are skipped by GIO, so the
whole thing degrades as the user curates the suite. Deviation from
the backlog text: viewers are a module toggle, not template package
lines — zathura's theming needs its HM module (the real-config
boundary of the toggle discipline).

V1: template-home generation asserted — mimeapps.list rendered, themed
zathurarc, binaries in home-path. V3 open-a-file smoke queued.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

modules/home/default.nix

@@ -23,6 +23,8 @@
     ./shell.nix     # zsh + starship + bat/eza/zoxide, themed
     ./keys.nix      # gpg-agent (fronts SSH) + pinentry-qt
     ./fastfetch.nix # system info with the themed Nomarchy logo
+    ./viewers.nix   # zathura (Stylix-themed) + imv — PDF/image viewing
+    ./mime.nix      # default applications (mimeapps.list), degrades with the suite
   ];
 
   # Clipboard history (wl-paste watcher); browsed via the SUPER+CTRL+V

modules/home/mime.nix

@@ -0,0 +1,48 @@
+# Default applications (xdg mimeapps.list) — without this, "open a
+# PDF/photo" falls to whatever GTK guesses first (GIMP for images).
+# Every association is mkDefault AND degrades gracefully by design: an
+# entry whose .desktop file isn't installed is skipped by GIO/xdg-open,
+# which then falls through to whatever else claims the type — so
+# deleting an app from the template suite (or never uncommenting the
+# browser) leaves no broken "open" behaviour, just the old guessing.
+{ config, lib, ... }:
+
+lib.mkIf config.nomarchy.mime.enable {
+  xdg.mimeApps = {
+    enable = lib.mkDefault true;
+    defaultApplications = lib.mapAttrs (_: v: lib.mkDefault v) {
+      "application/pdf" = "org.pwmt.zathura.desktop";
+
+      "image/png" = "imv.desktop";
+      "image/jpeg" = "imv.desktop";
+      "image/gif" = "imv.desktop";
+      "image/webp" = "imv.desktop";
+      "image/avif" = "imv.desktop";
+      "image/bmp" = "imv.desktop";
+      "image/tiff" = "imv.desktop";
+      "image/svg+xml" = "imv.desktop";
+
+      "video/mp4" = "mpv.desktop";
+      "video/webm" = "mpv.desktop";
+      "video/x-matroska" = "mpv.desktop";
+      "video/quicktime" = "mpv.desktop";
+      "audio/mpeg" = "mpv.desktop";
+      "audio/flac" = "mpv.desktop";
+      "audio/ogg" = "mpv.desktop";
+
+      # The template's active editor; degrades if you drop vscode.
+      "text/plain" = "code.desktop";
+
+      # The system-side Thunar (nomarchy.system.fileManager).
+      "inode/directory" = "thunar.desktop";
+
+      # The template ships no browser by default (open Decision) — these
+      # are inert until one is installed; firefox is the template's first
+      # suggestion. A different browser registers its own handler and
+      # wins once these entries stay dead.
+      "text/html" = "firefox.desktop";
+      "x-scheme-handler/http" = "firefox.desktop";
+      "x-scheme-handler/https" = "firefox.desktop";
+    };
+  };
+}

modules/home/options.nix

@@ -252,6 +252,8 @@ in
     btop.enable = lib.mkEnableOption "btop with the per-theme nomarchy theme" // { default = true; };
     stylix.enable = lib.mkEnableOption "Stylix theming for the long tail of apps (GTK, Qt, cursors)" // { default = true; };
     displays.enable = lib.mkEnableOption "the nwg-displays interactive monitor arranger (a helper to find nomarchy.monitors values; the declarative config stays the source of truth)" // { default = true; };
+    viewers.enable = lib.mkEnableOption "the document/image viewers (zathura, Stylix-themed, + imv)" // { default = true; };
+    mime.enable = lib.mkEnableOption "default file associations (xdg mimeapps.list: PDF/image/video/text/browser/directory); entries for absent apps are skipped, so it degrades with the package suite" // { default = true; };
 
     # ── Computed (read-only) ───────────────────────────────────────
     theme = lib.mkOption {

modules/home/stylix.nix

@@ -47,6 +47,8 @@ in
       targets = {
         gtk.enable = true;
         qt.enable = true;
+        # No-op unless programs.zathura is on (viewers.nix enables it).
+        zathura.enable = true;
       };
 
       cursor = {

modules/home/viewers.nix

@@ -0,0 +1,15 @@
+# Document & image viewers — the "open a PDF / open a photo" half of a
+# complete workstation. zathura goes through its HM module (not a bare
+# package) because Stylix themes it via programs.zathura.options — the
+# reason it's a component toggle here rather than a template package
+# line. imv rides along: wayland-native, and an image viewer is a
+# borderless dark surface — nothing to theme. The heavier editors
+# (GIMP, Inkscape) stay template packages; mime.nix points the default
+# associations at these viewers.
+{ config, lib, pkgs, ... }:
+
+lib.mkIf config.nomarchy.viewers.enable {
+  programs.zathura.enable = lib.mkDefault true;
+
+  home.packages = [ pkgs.imv ];
+}