fix(git): bypass external diff driver; preserve version pins and zizmor

- git: pass --no-ext-diff so difftastic/other diff.external drivers don't
  break --unified=0 parsing (was yielding zero ranges -> whole-file strip)
- config: add /regex/ preserve patterns; keep version pins (# v2.1.6) and
  zizmor: directives by default
- bump version to 0.4.2

internal/git/git.go

@@ -109,9 +109,9 @@ func GetUnstagedChanges() ([]FileChange, error) {
 func getLineRangesFromDiff(file string, staged bool) ([]LineRange, error) {
 	var cmd *exec.Cmd
 	if staged {
-		cmd = exec.Command("git", "diff", "--cached", "--unified=0", file)
+		cmd = exec.Command("git", "diff", "--no-ext-diff", "--cached", "--unified=0", file)
 	} else {
-		cmd = exec.Command("git", "diff", "--unified=0", file)
+		cmd = exec.Command("git", "diff", "--no-ext-diff", "--unified=0", file)
 	}
 
 	output, err := cmd.Output()

internal/git/git_test.go

@@ -1,9 +1,59 @@
 package git
 
 import (
+	"os"
+	"os/exec"
+	"path/filepath"
 	"testing"
 )
 
+func runGit(t *testing.T, dir string, args ...string) {
+	t.Helper()
+	cmd := exec.Command("git", args...)
+	cmd.Dir = dir
+	if out, err := cmd.CombinedOutput(); err != nil {
+		t.Fatalf("git %v: %v\n%s", args, err, out)
+	}
+}
+
+func TestGetLineRangesFromDiffIgnoresExternalDiff(t *testing.T) {
+	dir := t.TempDir()
+	runGit(t, dir, "init", "-q")
+	runGit(t, dir, "config", "user.email", "t@t")
+	runGit(t, dir, "config", "user.name", "t")
+	runGit(t, dir, "config", "diff.external", "true")
+
+	path := filepath.Join(dir, "f.py")
+	if err := os.WriteFile(path, []byte("a = 1\nb = 2\nc = 3\n"), 0644); err != nil {
+		t.Fatal(err)
+	}
+	runGit(t, dir, "add", "f.py")
+	runGit(t, dir, "commit", "-qm", "init")
+
+	if err := os.WriteFile(path, []byte("a = 1\nb = 2\nc = 3 changed\n"), 0644); err != nil {
+		t.Fatal(err)
+	}
+
+	wd, err := os.Getwd()
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.Chdir(wd)
+	if err := os.Chdir(dir); err != nil {
+		t.Fatal(err)
+	}
+
+	ranges, err := getLineRangesFromDiff("f.py", false)
+	if err != nil {
+		t.Fatalf("getLineRangesFromDiff: %v", err)
+	}
+
+	want := []LineRange{{Start: 3, End: 3}}
+	if len(ranges) != len(want) || ranges[0] != want[0] {
+		t.Fatalf("ranges = %v, want %v (external diff not bypassed)", ranges, want)
+	}
+}
+
 func TestParseGitDiffUnified(t *testing.T) {
 	tests := []struct {
 		name     string