feat: add Word and Excel preview in review UI

[NeoMei]

Issue for this PR

Closes #

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Adds native preview support for Word (.docx) and Excel (.xlsx) files in the review UI and file tabs. Previously these files were treated as binary and showed a generic "Binary file" message. Now they render as HTML so users can view their contents naturally.

Backend changes:

• Removed docx, xlsx, pptx from the binary file list in packages/opencode/src/file/index.ts.
• Added office extension recognition.
• Office files are now read and returned as base64-encoded text content.

UI changes:

• Added "office" to MediaKind in packages/ui/src/pierre/media.ts.
• Created OfficeViewer component (packages/ui/src/components/office-viewer.tsx):
  • Uses mammoth to convert .docx to semantic HTML.
  • Uses xlsx (SheetJS) to convert .xlsx sheets to HTML tables.
  • .pptx shows a "not supported yet" placeholder.
• Added office-viewer.css with basic typography and table styling.

App changes:

• Updated onError type in packages/app/src/pages/session/file-tabs.tsx to include "office" kind.

Fixes:

• Fixed broken symlink custom-elements.d.ts in packages/app and packages/enterprise that caused typecheck failures on Windows.

How did you verify your code works?

• Ran bun turbo typecheck — all 14 packages passed.
• Ran bun run build in packages/desktop — Vite build completed successfully (2293 modules transformed).
• Could not run live Tauri dev due to missing Rust (cargo) in the environment.

Screenshots / recordings

N/A — could not run the live desktop app in this environment.

Checklist

• I have tested my changes locally (typecheck + build)
• I have not included unrelated changes in this PR

[github-actions]

Thanks for updating your PR! It now meets our contributing guidelines. 👍

[NeoMei]

The unit (windows) failure is a pre-existing network issue unrelated to this PR:

error: TarballFailedToDownload downloading tarball ghostty-web@github:anomalyco/ghostty-web#main error: ghostty-web@github:anomalyco/ghostty-web#main failed to resolve

All other checks pass, including e2e (windows) which validates the symlink fix. Could a maintainer please re-trigger the failed job when convenient?