Add Fedora support, Qt6 SDDM theme and config fixes

[kaidozerotwo]

Summary

This adds a Fedora install path to the existing installer and fixes a few things that break on current releases of SDDM, Hyprland and Waybar. The Arch path stays the same apart from the Qt6 package names for SDDM.

Changes

Fedora support for the installer

• helper.sh detects Fedora and installs packages with dnf, the sdegler/hyprland COPR and per-user Flatpaks. Each module gets its own dnfpkgs.lst / flatpakpkgs.lst.
• AUR-only apps get Fedora stand-ins (fastfetch, rofimoji, nm-connection-editor, blueman). Apps with no equivalent are disabled.
• GDM stays unless the user opts in to SDDM, and the GRUB theme is skipped on Fedora.
• The installer asks before installing SDDM, Spotify and Vesktop, and the reboot prompt defaults to no.
• Files under $HOME are no longer written with sudo, so they stay user-owned.
• Appends are idempotent and safe on files with no trailing newline.
• NVIDIA env vars go to nvidia.conf, and a local.conf is sourced last so user tweaks survive reinstalls.
• The README has a new Fedora section.

SDDM theme on the Qt6 greeter
SDDM 0.21+ runs themes on Qt6, which has no QtQuick.Controls 1, Controls.Styles or Audio. Without a port, the theme fails to load and SDDM silently falls back to its embedded theme.

• Ported to Qt6 imports and QtQuick.Controls.Basic. The background and sounds are kept; the sounds now play through QtMultimedia SoundEffect.
• metadata.desktop sets QtVersion=6, and the package lists now use the Qt6 packages (qt6-declarative, qt6-multimedia, qt6-wayland).
• A failed login now shows a visible message and clears and refocuses the password field. A Caps Lock warning and the current keyboard layout are also shown, so a rejected password is obvious even with the sound muted.

Config fixes

• Waybar: removed a stray }, that closed the root object early and stopped the config from parsing. The memory module's right-click now opens missioncenter instead of the nonexistent missioncontrol.
• Hyprland 0.56 renamed misc:new_window_takes_over_fullscreen to misc:on_focus_under_fullscreen.
• Vesktop: the theme is installed under the filename that settings.json enables.

Testing

• Full install on Fedora 44 (GNOME Workstation, NVIDIA): Hyprland session, Waybar, Rofi, SDDM and Vesktop.
• Installer logic tested without installing packages (HYPRLAIN_SKIP_PACKAGES=1, a throwaway HOME, stubbed sudo/curl/flatpak).
• bash -n passes on every install script.
• SDDM theme: sddm-greeter-qt6 --test-mode loads it with no QML errors. As a control, a deliberately broken copy reports its error, which confirms the check can fail.
• The sound playback via SoundEffect has only been load-tested in test mode, not heard on a live login screen.
• Not tested on Arch. I don't have an Arch machine. The Arch-side changes are the Qt6 package names for SDDM and the shared helper changes, so a quick run of the SDDM module on Arch would be appreciated.