test(parser): migrate frontmatter_extraction_test.go to testify + add missing coverage

[Copilot]

pkg/parser/frontmatter_extraction_test.go used raw t.Errorf/t.Fatalf throughout and left ExtractWorkflowNameFromContent and ExtractWorkflowNameFromMarkdownBody entirely untested.

Testify migration

• Replaced all t.Errorf/t.Fatalf with require.NoError/require.Error/assert.Equal
• Dropped manual map iteration in TestExtractFrontmatterFromContent — replaced with a single assert.Equal on the whole map
• Removed reflect.DeepEqual + reflect import in favour of assert.Equal

// Before
if len(tt.wantYAML) != len(result.Frontmatter) {
    t.Errorf("frontmatter length = %v, want %v", ...)
}
for key, expectedValue := range tt.wantYAML {
    if actualValue, exists := result.Frontmatter[key]; !exists {
        t.Errorf("missing key %v", key)
    } else if actualValue != expectedValue {
        t.Errorf("frontmatter[%v] = %v, want %v", ...)
    }
}

// After
assert.Equal(t, tt.wantYAML, result.Frontmatter, "frontmatter should match expected")

New test coverage

• TestExtractWorkflowNameFromMarkdownBody — 6 cases: H1 found, trimmed whitespace, no H1 (filename fallback), empty body, H1 after prose, full-path fallback
• TestExtractWorkflowNameFromContent — 6 cases: H1 with frontmatter, H1 without frontmatter, no H1 fallback, empty content, unclosed frontmatter error, full-path fallback