Fixes#14608
## Summary
Fix printing issues when exporting documents while using the dark theme.
Previously, when printing or saving a document as PDF in dark mode, text
color was forced to black while some block containers (such as code
blocks and quotes) retained their dark backgrounds. This resulted in
**black text on dark backgrounds**, making the content unreadable in the
exported PDF.
## Changes
* Reset relevant CSS variables in the `@media print` section of
`print-to-pdf.ts`.
* Ensure block containers such as **code blocks and quotes** render with
light backgrounds during printing.
* Maintain readable text colors by forcing text color to black for print
output.
This approach updates the **CSS variables used by BlockSuite
components**, ensuring that elements relying on variables like
`--affine-background-code-block` and `--affine-quote-color` correctly
switch to light backgrounds in print mode.
## Result
Documents printed or exported as PDF from dark mode now render correctly
with:
* readable text
* proper light backgrounds for code blocks and quotes
* consistent formatting in print output
<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit
* **Style**
* Enhanced print-to-PDF styling for improved visual presentation of code
blocks, quotes, and borders when exporting or printing documents to
maintain better readability and consistency.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
Co-authored-by: sahilkhan09k <sahilkhan392005@gmail.com>
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