feat(home): NUR + firefox plasma integration

Install plasma-integration extension from NUR, add two settings to
enhance experience in KDE Plasma:

- disable media keys due to plasma-integration
- use KDE file picker over default GTK one

home/modules/plasma.nix

@@ -1,4 +1,14 @@
+{ pkgs, ... }:
 {
+  programs.firefox.profiles.default = {
+    extensions = [ pkgs.nur.repos.rycee.firefox-addons.plasma-integration ];
+
+    settings = {
+      "widget.use-xdg-desktop-portal.file-picker" = 1;
+      "media.hardwaremediakeys.enabled" = false;
+    };
+  };
+
   programs.plasma = {
     enable = true;
     overrideConfig = true;