refactor: address Copilot review suggestions

- Handle CRLF line endings in frontmatter detection (grep '^---' instead
  of '^---$')
- Fix double blank line after frontmatter in PowerShell New-AgentFile
- Remove unused tempfile import from tests
- Add encoding="utf-8" to all open() calls for cross-platform safety

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: fsilvaortiz

scripts/bash/update-agent-context.sh

@@ -503,7 +503,7 @@ update_existing_agent_file() {
 
     # Ensure Cursor .mdc files have YAML frontmatter for auto-inclusion
     if [[ "$target_file" == *.mdc ]]; then
-        if ! head -1 "$temp_file" | grep -q '^---$'; then
+        if ! head -1 "$temp_file" | grep -q '^---'; then
             local frontmatter_file
             frontmatter_file=$(mktemp) || { rm -f "$temp_file"; return 1; }
             printf '%s\n' "---" "description: Project Development Guidelines" "globs: [\"**/*\"]" "alwaysApply: true" "---" "" > "$frontmatter_file"

scripts/powershell/update-agent-context.ps1

@@ -261,7 +261,7 @@ function New-AgentFile {
     # Prepend Cursor frontmatter for .mdc files so rules are auto-included
     if ($TargetFile -match '\.mdc$') {
         $frontmatter = @('---','description: Project Development Guidelines','globs: ["**/*"]','alwaysApply: true','---','') -join [Environment]::NewLine
-        $content = $frontmatter + [Environment]::NewLine + $content
+        $content = $frontmatter + $content
     }
 
     $parent = Split-Path -Parent $TargetFile

tests/test_cursor_frontmatter.py

@@ -8,7 +8,6 @@
 import os
 import shutil
 import subprocess
-import tempfile
 import textwrap
 
 import pytest
@@ -40,14 +39,14 @@ class TestScriptFrontmatterPattern:
 
     def test_create_new_has_mdc_frontmatter_logic(self):
         """create_new_agent_file() must contain .mdc frontmatter logic."""
-        with open(SCRIPT_PATH) as f:
+        with open(SCRIPT_PATH, encoding="utf-8") as f:
             content = f.read()
         assert 'if [[ "$target_file" == *.mdc ]]' in content
         assert "alwaysApply: true" in content
 
     def test_update_existing_has_mdc_frontmatter_logic(self):
         """update_existing_agent_file() must also handle .mdc frontmatter."""
-        with open(SCRIPT_PATH) as f:
+        with open(SCRIPT_PATH, encoding="utf-8") as f:
             content = f.read()
         # There should be two occurrences of the .mdc check — one per function
         occurrences = content.count('if [[ "$target_file" == *.mdc ]]')
@@ -64,7 +63,7 @@ def test_powershell_script_has_mdc_frontmatter_logic(self):
             "powershell",
             "update-agent-context.ps1",
         )
-        with open(ps_path) as f:
+        with open(ps_path, encoding="utf-8") as f:
             content = f.read()
         assert "alwaysApply: true" in content
         occurrences = content.count(r"\.mdc$")