fix(hooks): repair conflict-marker check mangled by sed '&' expansion [#769]

Restores the intended tightened pattern: exact git markers only
(7-char = alone; <<<<<<< / >>>>>>> with optional ref). Decorative
==== banners no longer false-positive; check is fully functional again.

https://projects.knownelement.com/issues/769#note-4152

hooks/global/pre-commit

@@ -24,7 +24,7 @@ while IFS= read -r -d '' f; do
     esac
     [ -f "$REPO_ROOT/$f" ] || continue
 
-    if grep -nE '^(<{7}( \S+)?|=======|>{7}( \S+)?)$' "$REPO_ROOT/$f" >/dev/null 2>    if grep -nE '^(<<<<<<<|=======|>>>>>>>)' "$REPO_ROOT/$f" >/dev/null 2>&1; then1; then
+    if grep -nE '^(<{7}( \S+)?|=======|>{7}( \S+)?)$' "$REPO_ROOT/$f" >/dev/null 2>&1; then
         echo "FAIL conflict markers staged in $f" >&2; FAIL=1
     fi
     case "$f" in