fix: cross-platform CI test fixes and parse bug fix

- Add .gitattributes to force LF in mock files (Windows autocrlf)
- Fix parse.go: detect line endings from content instead of runtime.GOOS
- Add fail-fast: false to CI matrix; trigger on all branch pushes
- Skip chmod-based tests on Windows (permissions work differently)
- Use filepath.Join for expected paths in Windows path tests
- Use platform-appropriate invalid paths in error tests
- Add Windows absolute path test case for ValidateSheetName
- Skip Unix-specific integration tests on Windows

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

internal/sheet/copy_error_test.go

@@ -3,6 +3,7 @@ package sheet
 import (
 	"os"
 	"path/filepath"
+	"runtime"
 	"testing"
 )
 
@@ -130,6 +131,10 @@ func TestCopyIOError(t *testing.T) {
 
 // TestCopyCleanupOnError verifies that partially written files are cleaned up on error
 func TestCopyCleanupOnError(t *testing.T) {
+	if runtime.GOOS == "windows" {
+		t.Skip("chmod does not restrict reads on Windows")
+	}
+
 	// Create a source file that we'll make unreadable after opening
 	src, err := os.CreateTemp("", "copy-test-cleanup-*")
 	if err != nil {

internal/sheet/parse.go

@@ -2,7 +2,6 @@ package sheet
 
 import (
 	"fmt"
-	"runtime"
 	"strings"
 
 	"gopkg.in/yaml.v3"
@@ -11,9 +10,9 @@ import (
 // Parse parses cheatsheet frontmatter
 func parse(markdown string) (frontmatter, string, error) {
 
-	// determine the appropriate line-break for the platform
+	// detect the line-break style used in the content
 	linebreak := "\n"
-	if runtime.GOOS == "windows" {
+	if strings.Contains(markdown, "\r\n") {
 		linebreak = "\r\n"
 	}
 

internal/sheet/parse_extended_test.go

@@ -1,17 +1,11 @@
 package sheet
 
 import (
-	"runtime"
 	"testing"
 )
 
 // TestParseWindowsLineEndings tests parsing with Windows line endings
 func TestParseWindowsLineEndings(t *testing.T) {
-	// Only test Windows line endings on Windows
-	if runtime.GOOS != "windows" {
-		t.Skip("Skipping Windows line ending test on non-Windows platform")
-	}
-
 	// stub our cheatsheet content with Windows line endings
 	markdown := "---\r\nsyntax: go\r\ntags: [ test ]\r\n---\r\nTo foo the bar: baz"