Prevent inherited content color from being pasted

[SoftCreatR]

Summary

Prevent normal inherited WSC text color from being persisted as explicit font color when users copy and paste formatted text.

Ref: https://www.woltlab.com/community/thread/318933-graue-texte

Problem

Browsers serialize rich clipboard HTML with computed styles. Copying normal text from WSC in dark mode can produce clipboard HTML like:

<span style="color: rgb(209, 210, 211); ...">Text</span>

CKEditor treats this as intentional fontColor formatting and serializes it into stored content.

Solution

Add a clipboard sanitizer in WoltlabPasteFromOffice during ClipboardPipeline#inputTransformation, before CKEditor upcasts pasted HTML into model attributes.

The sanitizer removes color styles that match WSC’s inherited content text color (--wcfContentText) and keeps other formatting intact.

This is deliberately conservative: arbitrary external colors are not stripped, because browser clipboard HTML does not reliably distinguish inherited page color from intentionally colored author content.

Testing

Browser reproduction in Chrome:

• Copying normal WSC dark-mode text produced clipboard HTML with color: rgb(209, 210, 211).
• Without the fix, pasting serialized as:

<p><span style="color:rgb(209,210,211);">Wer anderen eine Bratwurst brät, hat ein Bratwurst-Bratgerät.</span></p>

• With the fix, pasting serialized as:

<p>Wer anderen eine Bratwurst brät, hat ein Bratwurst-Bratgerät.</p>

Additional checks:

• Default light content color is stripped.
• Custom --wcfContentText: rgb(85, 85, 85) is stripped.
• Bold text remains bold while only the inherited color is removed.
• Explicit external/non-WSC colors are preserved.