fix(build): improve Linux install script reliability and idempotency

- Fix tilde expansion: replace quoted '~' paths with $HOME so they
  actually resolve to the user's home directory instead of being
  treated literally
- Add existence checks before copying files so the script is
  idempotent and skips already-installed resources
- Add progress/status echo messages for each installation step
  so the user can see what is being done

build/install_linux.sh

@@ -1,26 +1,39 @@
 #!/bin/bash
 
 # copy desktop file
-if [ -e "~/.local/share/applications/AniTrack.desktop" ]; then
+if [ ! -f "$HOME/.local/share/applications/AniTrack.desktop" ]; then
   if [ -d "~/.local/share/applications/" ]; then
+    echo "Copying desktop file..."
     cp ./AniTrack.desktop ~/.local/share/applications/
   else
     mkdir -p ~/.local/share/applications/
+    echo "Copying desktop file..."
     cp ./AniTrack.desktop ~/.local/share/applications/
   fi
+else
+  echo "Desktop file already installed..."
 fi
 
 # copy icons to xdg folders
 for size in 32 48 64 128; do
+  if [ ! -f $HOME/.local/share/icons/hicolor/${size}x${size}/apps/AniTrack.png ]; then
+    echo "Installing ${size} icon size..."
     xdg-icon-resource install --novendor --context apps --size $size ./icon/$size/AniTrack.png AniTrack
+  else
+    echo "${size} icon size already exists..."
+  fi
 done
 
 # copy AniTrack Binary to $HOME/Applications/
-if ! [ -d "~/Applications" ]; then
+if ! [ -d "$HOME/Applications" ]; then
   mkdir -p ~/Applications
+  echo "Installing app to ~/Applications..."
   cp ./bin/AniTrack ~/Applications/
-elif ! [[ -e ~/Applications/AniTrack ]]; then
+elif ! [[ -e $HOME/Applications/AniTrack ]]; then
+  echo "Installing app to ~/Applications"
   cp ./bin/AniTrack ~/Applications/
+else
+  echo "AniTrack already in Applications..."
 fi
 
 echo "AniTrack has been successfully installed."