fix(super-editor): normalize API tab insertions

[missysuperdoc]

What changed

• normalize API text writes so literal tab characters are materialized as structured inline tab nodes instead of raw text
• reuse the same inline-content expansion for direct writes, tracked insertions, and text execution in the document API write paths
• add regression coverage for direct writes, tracked changes, and exported DOCX XML in both direct and tracked adapter flows

Why this changed

API-driven insertions were preserving \t inside text nodes, which exported to raw tab characters inside <w:t> instead of proper <w:tab/> runs.

Impact

API insertions now match the editor's native tab model, and DOCX export emits valid Word tab runs for both direct and tracked document API writes.

Validation

• pnpm --prefix packages/super-editor exec vitest run src/editors/v1/document-api-adapters/write-adapter.test.ts
• pnpm --prefix packages/super-editor exec vitest run src/editors/v1/extensions/track-changes/track-changes-extension.test.js
• pnpm --prefix packages/super-editor exec vitest run src/editors/v1/document-api-adapters/write-tabs-export.integration.test.ts