Revert "fix: remove pasted text/background colors in Tiptap editor"

[AlexAndBear]

Description

Reverts #3275 because stripping text and background colors from pasted HTML also removes those colors when users copy selected text from our editor. That loses existing editor formatting in a case where users would not expect it, which is too large a downside for this behavior.

Specifically, this removes the pasted HTML color-stripping helper, its export, the Tiptap transformPastedHTML hook, and the related unit test.

Related Issue

• Reverts fix: remove pasted text/background colors in Tiptap editor #3275

How Has This Been Tested?

• test environment: local macOS development environment, pnpm + vitest
• test case 1: pnpm --config.confirmModulesPurge=false test:unit --run packages/web-pkg/tests/unit/editor/composables/useTextEditor.spec.ts
• test case 2: confirmed there are no remaining references to stripColorFormattingFromPastedHtml or transformPastedHTML in the editor package
• ...

Types of changes

• Bugfix
• Enhancement (a change that doesn't break existing code or deployments)
• Breaking change (a modification that affects current functionality)
• Technical debt (addressing code that needs refactoring or improvements)
• Tests (adding or improving tests)
• Documentation (updates or additions to documentation)
• Maintenance (like dependency updates or tooling adjustments)