Switch desktop environment from Hyprland to Budgie; app/audio overhaul

Hyprland problems prompted a full switch to Budgie (X11, lightdm).
Removes every Hyprland/Quickshell dotfile, theming script, and
hypr-specific module (theme.nix, the whole scripts/ theming pipeline,
hyprland.conf/hyprpaper.conf, the Quickshell shell QML, kitty/mako/
rofi configs) in favor of Budgie's own panel/session/theming and a
GSettings-driven icon/cursor override.

App changes:
- Konsole/Dolphin replace kitty/Thunar as the default terminal and
  file manager; dropped xterm too (services.xserver.excludePackages)
- Added Okular (PDF/document viewer), KCalc (calculator), Elisa
  (audio player) -- nothing filled those roles before
- Added OBS Studio

Audio/voice:
- EasyEffects for real-time mic/output effects (creates its own
  selectable "Easy Effects Source" virtual mic automatically)
- A standalone "Virtual Microphone" PipeWire device (loopback module,
  services.pipewire.extraConfig), fully independent of the real mic,
  for routing EasyEffects/Soundux output separately from what Discord
  etc. use by default
- qpwgraph for manual patchbay routing into the above
- Soundux (soundboard) installed via Flatpak -- no longer packaged in
  this nixpkgs channel

default-apps.nix: Okular wired into mimeapps.list alongside the
existing Gwenview/Ark defaults; removed the Thunar-specific
"Open Terminal Here" custom-action tmpfiles rule (dead now that
Thunar's gone -- Dolphin gets the same via its built-in konsolepart
terminal panel for free).

modules/drivers.nix

@@ -10,14 +10,9 @@
   #OpenTabletDriver
   hardware.opentabletdriver.enable = true;
   hardware.uinput.enable = true;
-  boot.kernelModules = [ "uinput" "v4l2loopback" ];
+  boot.kernelModules = [ "uinput" ];
 
-  # Virtual webcam device so ffmpeg (fed by the GoPro's stream) can appear
-  # as a normal camera to apps like Discord. exclusive_caps=1 is required
-  # for Chromium/WebRTC-based apps to recognize it as a real capture device.
-  boot.extraModulePackages = [ config.boot.kernelPackages.v4l2loopback ];
   boot.extraModprobeConfig = ''
-    options v4l2loopback devices=1 video_nr=10 card_label="GoPro Webcam" exclusive_caps=1
     # PS4/PS5 controllers (e.g. DualSense) connect over Bluetooth then
     # immediately disconnect — a well-known Linux Bluetooth stack issue
     # where many adapters' Enhanced Retransmission Mode implementation is