refactor: group stow packages into common, mac and kde

Split the packages by platform so each app stays an opt-in Stow package
under common/, mac/ or kde/. KDE gets its own Fastfetch, Helium and
Spectacle packages, and darwin-breeze becomes kde/theme. The READMEs
document stowing a whole group as well as individual packages.

kde/tray-icons/README.md

@@ -0,0 +1,53 @@
+# Tray icons that match Breeze
+
+```sh
+stow -d kde -t "$HOME" tray-icons
+```
+
+Some icons need one more step after stowing; see below.
+
+## Ngó Sen (fcitx5-ngosen)
+
+Replaces Ngó Sen's monochrome tray icons with a V/E inside a rounded frame.
+
+```sh
+sudo ~/.local/share/ngosen-breeze-icons/install.sh
+~/.local/share/ngosen-breeze-icons/restart-fcitx5.sh
+systemctl --user restart plasma-plasmashell
+```
+
+- Ngó Sen points the tray at `/usr/share/icons/hicolor`, but Plasma looks
+  the icon up by name in the `breeze`/`breeze-dark` themes under
+  `/usr/share` and ignores `~/.local/share/icons`, so the system files have
+  to be replaced.
+- `install.sh` copies the icons and `apply.sh` to
+  `/usr/local/share/ngosen-breeze-icons/`, installs the pacman hook
+  `/etc/pacman.d/hooks/ngosen-breeze-icons.hook` to re-apply them after
+  every package upgrade, and sets `UseLotusIcons=False` and
+  `IconTheme=Dark` in `~/.config/fcitx5/conf/ngosen.conf`.
+- The original icons are kept in `/usr/local/share/ngosen-breeze-icons/orig/`;
+  `sudo ~/.local/share/ngosen-breeze-icons/restore.sh` puts them back and
+  removes the hook.
+- On KDE Wayland don't start fcitx5 with `fcitx5 -d`; use
+  `restart-fcitx5.sh` so KWin launches it.
+
+## qBittorrent
+
+`qbittorrent-tray-mono.svg` is qBittorrent's monochrome tray icon scaled
+down to 78%, so it has the same padding as Breeze status icons instead of
+filling the whole tray slot.
+
+qBittorrent 5.x only looks the tray icon up in the icon theme when "Use
+icons from system theme" is on, so also set (qBittorrent closed, or via
+Tools > Options > Behavior):
+
+```ini
+# ~/.config/qBittorrent/qBittorrent.conf
+[Appearance]
+TrayIconStyle=Monochrome
+
+[Preferences]
+Advanced\useSystemIconTheme=true
+```
+
+`qBittorrent.conf` itself isn't stowed: qBittorrent rewrites it on exit.