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

[gpardhivvarma]

Summary

Closes #2803

• Thread alternateHeaders from document settings (w:evenAndOddHeaders) through the layout engine so the paginator selects the correct header/footer variant per page
• Fix getVariantTypeForPage to use document page number (not section-relative) for even/odd selection, matching the rendering side (headerFooterUtils.ts)
• Add 4 unit tests covering variant selection, default behavior, and titlePg interaction

Problem

Documents with "Different Odd & Even Pages" enabled render the same header/footer on every page. The layout engine hardcoded alternateHeaders = false, preventing correct margin calculations for odd vs even page headers.

Changes

File	Change
layout-engine/src/index.ts	Add alternateHeaders to LayoutOptions, replace hardcoded false, fix getVariantTypeForPage to use document page number for even/odd
layout-engine/src/index.test.ts	4 tests: even/odd selection, default false, omitted defaults, titlePg + alternateHeaders
PresentationEditor.ts	Thread converter.pageStyles.alternateHeaders into layout options
types.ts	Add alternateHeaders to ResolvedLayoutOptions

What was already working (no changes needed)

• Import: w:evenAndOddHeaders parsed from settings.xml
• Layout Bridge: getHeaderFooterTypeForSection() handles even/odd variant selection
• Rendering: provider pattern renders whichever variant is selected
• Export: settings.xml preserved as-is

Test plan

• bun test in layout-engine — 581/581 passing
• 4 new alternateHeaders tests verify margin calculation per variant
• Manual verification with a Word doc using "Different Odd & Even Pages"

[gpardhivvarma]

@caio-pizzol