refactor: extract terminal launch logic into shared script

Add terminal-launcher script as a single entry point for launching
foot-based terminals with a given class and command. Migrate all
.desktop files to use it instead of inline foot invocations.

Simplify hyprland keybindings by replacing inline focus_or_launch
with hl.dsp.exec_cmd

script/terminal-launcher

@@ -0,0 +1,5 @@
+#!/bin/sh
+class=$1
+cmd=$2
+terminal="foot -a $class -T $class \"$cmd\""
+hyprctl dispatch "focus_or_launch({ match = '$class', cmd = 'foot -a $class -T $class $cmd'})"