Add Qt/GTK2 theming, default apps, LibreOffice; fix display.conf race

- Add qt-theme-set: a working Qt theming pipeline via qt6ct (the
  QT_QPA_PLATFORMTHEME=qt6ct env var was pointing at a platform theme
  plugin that wasn't even installed, so every Qt app fell back to its
  own default style). Also regenerates kdeglobals' KColorScheme groups
  and sets QT_QUICK_CONTROLS_STYLE=org.kde.desktop for Kirigami-based
  KDE apps, whose QML-drawn chrome ignores QPalette/qt6ct entirely.
  Gwenview's dialogs/content now follow the theme; its toolbar/statusbar
  chrome is a known remaining gap tied to Kirigami's platform-theme
  detection outside a full Plasma session
- Add GTK2 compat (~/.gtkrc-2.0: icon theme + font follow the theme;
  no dark variant exists for GTK2's Adwaita engine)
- Add modules/default-apps.nix: Gwenview/Ark as system-default image
  viewer/archive manager via /etc/xdg/mimeapps.list, LibreOffice
  (Qt6 build), and a working Thunar "Open Terminal Here" (it shipped
  calling exo-open, which isn't installed and never resolved)
- Fix display-set.sh: mktemp defaulted to /tmp, a different filesystem
  than ~/.config/hypr here, making the mv into display.conf a
  non-atomic copy+unlink. Hyprland's file watcher could catch it
  mid-replace and throw "source= globbing error: found no match" on
  any monitor mode/orientation change. Stress-tested with 60 concurrent
  write+reload cycles after the fix with zero errors

modules/scripts/display-set.sh

@@ -25,7 +25,15 @@ touch "$conf"
 
 line="monitor = $descriptor"
 if grep -q "^monitor = $mon," "$conf" 2>/dev/null; then
-    tmp=$(mktemp)
+    # mktemp in the same directory as $conf, not the default /tmp: /tmp is
+    # a different filesystem here, which makes `mv` below a non-atomic
+    # copy+unlink instead of a rename — Hyprland's file watcher (it
+    # watches every `source=`d file, including this one) could catch the
+    # destination mid-replace and its `source=` glob would find nothing,
+    # throwing "globbing error: found no match" (observed live after an
+    # orientation change, which always hits this branch since DP-1
+    # already has an existing line by then).
+    tmp=$(mktemp "$conf.XXXXXX")
     awk -v prefix="monitor = $mon," -v newline="$line" '
         index($0, prefix) == 1 { print newline; next } { print }
     ' "$conf" > "$tmp"

modules/scripts/gtk-theme-set.sh

@@ -117,3 +117,16 @@ if command -v dconf >/dev/null 2>&1; then
     dconf write /org/gnome/desktop/interface/icon-theme "'$icon_theme'"
     dconf write /org/gnome/desktop/interface/color-scheme "'$color_scheme'"
 fi
+
+# GTK2 compat: separate config format (~/.gtkrc-2.0, not settings.ini),
+# and no live theme-switching mechanism at all — GTK2 apps only read this
+# at their own startup. Only icon theme and font actually follow the
+# current theme; gnome-themes-extra's bundled GTK2 Adwaita engine has no
+# dark variant to switch to (GTK2 predates that concept), so gtk-theme-
+# name here is always the one real option, not a broken attempt at dark
+# mode.
+cat > "$HOME/.gtkrc-2.0" <<EOF
+gtk-theme-name="Adwaita"
+gtk-icon-theme-name="$icon_theme"
+gtk-font-name="Noto Sans 10"
+EOF

modules/scripts/qt-theme-set.sh

@@ -0,0 +1,105 @@
+#!/usr/bin/env bash
+# Regenerates qt6ct's config + color scheme to match the current Quickshell
+# theme, the Qt-side equivalent of gtk-theme-set. Qt apps (Gwenview, Ark,
+# Kate, ...) had no working platform theme plugin at all before this — the
+# QT_QPA_PLATFORMTHEME=qt6ct env var (hyprland.conf) was pointing at a
+# plugin that wasn't even installed, so every Qt app fell back to
+# whatever default style/palette it shipped with, ignoring the rest of
+# the desktop entirely. style=Fusion (not a KDE/Breeze style) matters
+# specifically: Fusion paints straight from QPalette, so a custom color
+# scheme here is guaranteed to actually show — Breeze-family styles
+# prefer reading colors from kdeglobals instead, which is a separate,
+# static, unrelated leftover file on this machine.
+set -euo pipefail
+
+accent="${1:?usage: qt-theme-set <accent> <bg> <bgAlt> <fg> <fgDim> <border> <dark:1|0>}"
+bg="${2:?bg required}"
+bg_alt="${3:?bgAlt required}"
+fg="${4:?fg required}"
+fg_dim="${5:?fgDim required}"
+border="${6:?border required}"
+dark="${7:?dark required}"
+
+dir="$HOME/.config/qt6ct"
+mkdir -p "$dir/colors"
+
+# qt6ct color scheme files store QPalette::ColorRole values as a fixed-
+# order, comma-separated #aarrggbb list — order and format verified
+# against the example schemes qt6ct itself ships
+# (share/qt6ct/colors/darker.conf etc.), not guessed: WindowText, Button,
+# Light, Midlight, Dark, Mid, Text, BrightText, ButtonText, Base, Window,
+# Shadow, Highlight, HighlightedText, Link, LinkVisited, AlternateBase,
+# NoRole, ToolTipBase, ToolTipText, PlaceholderText.
+a() { printf '#ff%s' "${1#\#}"; }  # opaque
+t() { printf '#80%s' "${1#\#}"; }  # translucent, for PlaceholderText
+
+active="$(a "$fg"), $(a "$bg_alt"), $(a "$border"), $(a "$bg_alt"), $(a "$bg"), $(a "$border"), $(a "$fg"), $(a "$fg"), $(a "$fg"), $(a "$bg"), $(a "$bg"), $(a "$border"), $(a "$accent"), $(a "$bg"), $(a "$accent"), $(a "$accent"), $(a "$bg_alt"), $(a "$bg"), $(a "$bg_alt"), $(a "$fg"), $(t "$fg_dim")"
+disabled="$(a "$fg_dim"), $(a "$bg_alt"), $(a "$border"), $(a "$bg_alt"), $(a "$bg"), $(a "$border"), $(a "$fg_dim"), $(a "$fg_dim"), $(a "$fg_dim"), $(a "$bg"), $(a "$bg"), $(a "$border"), $(a "$accent"), $(a "$fg_dim"), $(a "$accent"), $(a "$accent"), $(a "$bg_alt"), $(a "$bg"), $(a "$bg_alt"), $(a "$fg_dim"), $(t "$fg_dim")"
+
+color_file="$dir/colors/quickshell-theme.conf"
+cat > "$color_file" <<EOF
+[ColorScheme]
+active_colors=$active
+disabled_colors=$disabled
+inactive_colors=$active
+EOF
+
+icon_theme="Gruvbox-Plus-Light"
+[ "$dark" = "1" ] && icon_theme="Gruvbox-Plus-Dark"
+
+cat > "$dir/qt6ct.conf" <<EOF
+[Appearance]
+style=Fusion
+icon_theme=$icon_theme
+custom_palette=true
+color_scheme_path=$color_file
+standard_dialogs=default
+EOF
+
+# qt6ct's palette only reaches classic QWidget UI. Modern KDE apps
+# (confirmed live: Gwenview) draw their toolbar/chrome with Kirigami/QML
+# instead, which ignores QPalette entirely and reads kdeglobals' color
+# groups directly via KColorScheme — so without this, qt6ct alone left
+# exactly that chrome stuck on whatever this machine's stale leftover
+# kdeglobals had (unrelated purple KDE colors from some earlier install),
+# while everything else (dialogs, the actual image viewport, ...)
+# correctly followed the theme.
+rgb() {
+    local hex="${1#\#}"
+    printf '%d,%d,%d' "0x${hex:0:2}" "0x${hex:2:2}" "0x${hex:4:2}"
+}
+
+cat > "$HOME/.config/kdeglobals" <<EOF
+[General]
+ColorScheme=QuickshellTheme
+widgetStyle=Fusion
+
+[KDE]
+widgetStyle=Fusion
+
+[Colors:Window]
+BackgroundNormal=$(rgb "$bg_alt")
+ForegroundNormal=$(rgb "$fg")
+
+[Colors:View]
+BackgroundNormal=$(rgb "$bg")
+ForegroundNormal=$(rgb "$fg")
+
+[Colors:Button]
+BackgroundNormal=$(rgb "$bg_alt")
+ForegroundNormal=$(rgb "$fg")
+
+[Colors:Selection]
+BackgroundNormal=$(rgb "$accent")
+ForegroundNormal=$(rgb "$bg")
+DecorationFocus=$(rgb "$accent")
+DecorationHover=$(rgb "$accent")
+
+[Colors:Tooltip]
+BackgroundNormal=$(rgb "$bg_alt")
+ForegroundNormal=$(rgb "$fg")
+
+[Colors:Header]
+BackgroundNormal=$(rgb "$bg_alt")
+ForegroundNormal=$(rgb "$fg")
+EOF