Add copilot config, git-lfs setup, and per-file copilot symlinking

- Add copilot/config.yaml for Copilot CLI model preference
- Add git-lfs filter config to gitconfig
- Update setup script to symlink copilot files individually,
  preserving runtime data in ~/.copilot/

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: arthurnn

copilot/config.yaml

@@ -0,0 +1 @@
+model: claude-opus-4.5

gitconfig

@@ -46,3 +46,8 @@
 [credential "https://gist.github.com"]
 	helper = 
 	helper = !/usr/bin/gh auth git-credential
+[filter "lfs"]
+	clean = git-lfs clean -- %f
+	smudge = git-lfs smudge -- %f
+	process = git-lfs filter-process
+	required = true

script/setup

@@ -39,7 +39,8 @@ for DOTFILE in *; do
   fi
 
   # Don't try to install documentation/script files
-  echo $DOTFILE | egrep -q '(^script/$|\.txt$|\.md$|Dockerfile$)' && continue
+  # Skip copilot/ - handled separately to preserve runtime data
+  echo $DOTFILE | egrep -q '(^script/$|^copilot/$|\.txt$|\.md$|Dockerfile$)' && continue
 
   # Fixup VSCode settings path
   echo $DOTFILE | grep -q 'vscode-settings' &&
@@ -82,3 +83,13 @@ done
 # then
 #   ln -sf "$DOTFILESDIR" "$HOMEDOTFILES"
 # fi
+
+# Symlink Copilot config files individually (not the whole folder)
+if [ $UNIX ]
+then
+  mkdir -p "$HOME/.copilot"
+  for COPILOTFILE in "$DOTFILESDIR/copilot/"*; do
+    BASENAME=$(basename "$COPILOTFILE")
+    ln -sfv "$COPILOTFILE" "$HOME/.copilot/$BASENAME"
+  done
+fi