fix(print): render page with white background

[Resurgamz]

在打印时调用 renderToImage（Qt：:white），确保打印页面使用不透明白色背景。

Log：修复打印预览页面背景透明的问题，泣染页面图像时指定 Qt：:white 作为背景色。
Bug: https://pms.uniontech.com/bug-view-221301.html

[sourcery-ai]

Reviewer's guide (collapsed on small PRs)

Reviewer's Guide

This PR updates the print dialog invocation so that the rendered page image uses a white background instead of the default, ensuring consistent visual output when printing.

Sequence diagram for printing a page with a white background

sequenceDiagram
  actor User
  participant TopTilte
  participant DrawBoard
  participant Page
  participant PageContext
  participant CPrintManager

  User->>TopTilte: trigger print action
  TopTilte->>DrawBoard: currentPage()
  DrawBoard-->>TopTilte: Page
  TopTilte->>Page: context()
  Page-->>TopTilte: PageContext
  TopTilte->>PageContext: renderToImage(Qt::white)
  PageContext-->>TopTilte: imageWithWhiteBackground
  TopTilte->>CPrintManager: showPrintDialog(imageWithWhiteBackground, topMainWindowWidget, pageName)

Loading

File-Level Changes

Change	Details	Files
Ensure the page image passed to the print dialog is rendered with a white background.	Modify the call to render the current page image to pass Qt::white as the background color parameter. Keep the existing print dialog flow, including null checks for the page and its context, unchanged.	src/frame/toptoolbar.cpp

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[sourcery-ai]

Hey - I've left some high level feedback:

• Consider whether forcing a white background is always desired or if the print background color should be configurable or derived from the page/theme instead of hardcoded.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- Consider whether forcing a white background is always desired or if the print background color should be configurable or derived from the page/theme instead of hardcoded.

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[deepin-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: Resurgamz

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