feat: enable odd/even header-footer support (w:evenAndOddHeaders)

[gpardhivvarma]

What

Word documents with "Different Odd & Even Pages" enabled (w:evenAndOddHeaders in word/settings.xml) render the same header/footer on every page in SuperDoc. The even/odd variants are ignored.

Root Cause

The layout engine hardcodes alternateHeaders = false at packages/layout-engine/layout-engine/src/index.ts:1287, preventing the paginator from selecting the correct header/footer variant per page. This causes incorrect margin calculations — the body content area doesn't account for different header heights on odd vs even pages.

The rest of the pipeline already supports this:

• Import: w:evenAndOddHeaders is parsed from settings.xml → styles.alternateHeaders
• Layout Bridge: getHeaderFooterTypeForSection() already handles even/odd variant selection
• Rendering: The provider pattern renders whichever variant is selected

Expected Behavior

• Page 1 (odd): renders odd/default header
• Page 2 (even): renders even header
• Page 3 (odd): renders odd/default header
• Margins adjust per page based on actual header/footer content height for each variant

Spec Reference

• ECMA-376 §17.10 — Headers and Footers
• w:evenAndOddHeaders element in word/settings.xml

[linear]

IT-919