test(coverage): add targeted tests to raise per-package coverage gates

- internal/homesick/version: new version_test.go covers String constant
  and semver format validation
- internal/homesick/cli: add list, generate, clone, status, diff, and
  git-repo helper tests; coverage raised from 62.5% to 71.2%
- internal/homesick/core: new helpers_test.go covers runGit pretend,
  actionVerb, sayStatus, unlinkPath, linkPath, readSubdirs,
  matchesIgnoredDir, confirmDestroy, ExecAll edge cases, and
  Link/Unlink default castle wrappers; core_test.go and pull_test.go
  extended with New constructor and PullAll quiet-mode tests;
  exec_test.go extended with ExecAll no-repos-dir and error-wrap tests;
  coverage raised from 75.6% to 80.2%

internal/homesick/version/version_test.go

@@ -0,0 +1,21 @@
+package version
+
+import (
+	"regexp"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestStringConstant(t *testing.T) {
+	// Test that the version constant is not empty
+	assert.NotEmpty(t, String, "version.String should not be empty")
+}
+
+func TestStringMatchesSemVer(t *testing.T) {
+	// Test that the version string matches semantic versioning pattern (major.minor.patch)
+	semverPattern := `^\d+\.\d+\.\d+$`
+	matched, err := regexp.MatchString(semverPattern, String)
+	assert.NoError(t, err, "regex should be valid")
+	assert.True(t, matched, "version.String should match semantic versioning pattern (major.minor.patch), got: %s", String)
+}