install: use EXIT trap for temp directory cleanup

Replace scattered rm -rf calls with a single EXIT trap to ensure the
temp directory is always cleaned up on exit. Previously, failures in
curl/wget download, tar extraction, chmod, or mkdir left temp files
behind because set -e would exit before reaching manual cleanup calls.

The trap fires on any exit (success or failure), so it covers all
paths with one line while removing five redundant cleanup calls.

Author: marcelsafin

install.sh

@@ -75,14 +75,14 @@ echo "Downloading from: $DOWNLOAD_URL"
 
 # Download and extract with error handling
 TMP_DIR="$(mktemp -d)"
+trap 'rm -rf -- "$TMP_DIR"' EXIT
 TMP_TARBALL="$TMP_DIR/copilot-${PLATFORM}-${ARCH}.tar.gz"
 if command -v curl >/dev/null 2>&1; then
   curl -fsSL "${CURL_AUTH[@]}" "$DOWNLOAD_URL" -o "$TMP_TARBALL"
 elif command -v wget >/dev/null 2>&1; then
   wget -qO "$TMP_TARBALL" "${WGET_AUTH[@]}" "$DOWNLOAD_URL"
 else
   echo "Error: Neither curl nor wget found. Please install one of them."
-  rm -rf "$TMP_DIR"
   exit 1
 fi
 
@@ -101,15 +101,13 @@ if [ "$CHECKSUMS_AVAILABLE" = true ]; then
       echo "✓ Checksum validated"
     else
       echo "Error: Checksum validation failed." >&2
-      rm -rf "$TMP_DIR"
       exit 1
     fi
   elif command -v shasum >/dev/null 2>&1; then
     if (cd "$TMP_DIR" && shasum -a 256 -c --ignore-missing SHA256SUMS.txt >/dev/null 2>&1); then
       echo "✓ Checksum validated"
     else
       echo "Error: Checksum validation failed." >&2
-      rm -rf "$TMP_DIR"
       exit 1
     fi
   else
@@ -120,7 +118,6 @@ fi
 # Check that the file is a valid tarball
 if ! tar -tzf "$TMP_TARBALL" >/dev/null 2>&1; then
   echo "Error: Downloaded file is not a valid tarball or is corrupted." >&2
-  rm -rf "$TMP_DIR"
   exit 1
 fi
 
@@ -144,7 +141,6 @@ fi
 tar -xz -C "$INSTALL_DIR" -f "$TMP_TARBALL"
 chmod +x "$INSTALL_DIR/copilot"
 echo "✓ GitHub Copilot CLI installed to $INSTALL_DIR/copilot"
-rm -rf "$TMP_DIR"
 
 # Check if installed binary is accessible
 if ! command -v copilot >/dev/null 2>&1; then