fix: suppress spacing before after manual page breaks

[leandrotcawork]

Summary

This fixes a Word layout fidelity issue where the first real paragraph after an explicit manual page break could render too low in SuperDoc because paragraph spacingBefore was still applied at the fresh page top.

The change keeps the scope intentionally narrow:

• avoid synthesizing an empty paragraph when a ProseMirror paragraph only contributes page/column break layout blocks
• suppress spacingBefore only for paragraphs that start a fresh page immediately after an explicit manual page break
• preserve pageBreakBefore behavior, where paragraph spacing should still apply
• apply the suppression before float remeasurement so paragraph-anchored images/drawings use the actual page-top Y when computing available line widths

Why

In Word, an explicit manual page break starts the following paragraph at the top of the new page content area. SuperDoc could retain the following paragraph's spacingBefore, creating a visible gap above headings or other first-page content after the break.

The issue was especially visible in a DOCX fixture with a heading immediately after a manual page break: removing the gap manually in the editor also removed the intended paragraph border/line, which pointed to paragraph spacing/layout state rather than a painter-only issue.

Implementation Notes

• pm-adapter now skips fallback empty paragraph creation when the converted paragraph contains only break blocks.
• layoutDocument detects manual page breaks before a target paragraph, including paragraph-anchored images/drawings between the break and the paragraph.
• layoutParagraphBlock suppresses spacingBefore only when the paragraph is still at the top of a fresh page, before float scans and remeasurement.
• Page/margin-relative anchored object behavior is intentionally left unchanged in this PR.

Reference Document

DC_Template_Descricao_Cargo.docx

[chatgpt-codex-connector]

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