fix: normalize CRLF in email-strategist + guard linter against CRLF

marketing/marketing-email-strategist.md (#509) landed with CRLF line
endings, which violate .gitattributes (*.md text eol=lf) and broke
./scripts/lint-agents.sh — head -1 saw "---\r" and reported a confusing
"missing frontmatter opening ---" on a file that visibly starts with ---.

- Normalize that file to LF (content-neutral; 0 non-whitespace changes).
- Add a CRLF guard to lint-agents.sh that fails fast with a clear,
  actionable message instead of the misleading frontmatter error.

Thanks @hedonnn for the Email Marketing Strategist agent — great content;
just needed the line endings normalized.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

scripts/lint-agents.sh

@@ -58,6 +58,15 @@ lint_file() {
     return
   fi
 
+  # 0. Reject CRLF line endings (repo standard is LF — see .gitattributes).
+  # A trailing \r otherwise makes the frontmatter check below fail with a
+  # confusing "missing frontmatter ---" even when the file clearly starts ---.
+  if LC_ALL=C grep -q $'\r' "$file"; then
+    echo "ERROR $file: CRLF line endings detected — convert to LF (e.g. 'perl -i -pe \"s/\\r\$//\" $file'); repo uses LF per .gitattributes"
+    errors=$((errors + 1))
+    return
+  fi
+
   # 1. Check frontmatter delimiters
   local first_line
   first_line=$(head -1 "$file")