Fix file previews and workspace UI details

[mssssss123]

Summary

• Fix creating a file or folder in an empty project and align the sidebar header with the workspace header.
• Normalize equivalent drawing XML namespace prefixes before ExcelJS parses XLSX workbooks. Show actionable spreadsheet preview errors in the file pane without a duplicate generic 500 toast.
• Start Word previews with the outline collapsed, while keeping the toolbar toggle available.
• Refine scrolling and top spacing in the create-workspace dialog.

These are selective UI fixes inspired by #592. This PR does not include its onboarding model-configuration changes.

Verification

• pnpm --dir ui exec vitest run server/services/spreadsheetPreview.test.js src/components/code-editor/view/subcomponents/CodeEditorBinaryFile.test.tsx src/components/code-editor/view/subcomponents/DocxBuiltinPreview.test.tsx src/utils/api.preview.test.js
• pnpm --dir ui run typecheck
• pnpm --dir ui run build
• Opened the previously failing Borealis workbook in the local app and confirmed all seven worksheet tabs load.
• Opened a Word document in the local app and confirmed the outline starts collapsed and can be expanded.
• Checked the create-workspace dialog at normal and short viewport heights; the shorter view remains scrollable.