fix(import): preserve preformatted text node newlines

[DavidBabinec]

What changed

• Preserve literal whitespace for no-wrapper base.text nodes in both publisher output and the editor canvas.
• Keep authored hard line breaks unchanged for semantic text elements such as headings and paragraphs.
• Add regression coverage for <pre><code> imports and document the whitespace-preservation contract.

Why

Super Import correctly stored significant newlines inside <pre>, but the shared text renderer published those no-wrapper newline nodes as <br> elements. Typewriter scripts that snapshot code.childNodes then saw empty element segments; reading past those segments produced the literal text undefined throughout imported terminal/code animations.

Impact

Imported preformatted blocks retain the source DOM text-node shape, so runtime scripts can safely inspect and animate them. Existing imported sites only need to be republished after upgrading; no re-import is required.

Verification

• bun test — 6,281 passed
• bun run lint
• bun run build
• bun run doctor — completed with the repository's existing warning baseline