Use instance time zone for all data export time fields

Objective

• Reports Hub / data export downloads should show every time-based column in the company’s instance time zone (e.g. Eastern for an Eastern-configured org), not a mismatched offset that forces spreadsheet math.

Background

• SE request: exports were observed “not in Eastern or Central” when users expected local business time.
• Company default TZ lives on attik-backend/src/models/companySchema.ts (timezone, default America/Denver).
• Generation flows through src/routes/dataExport.ts with cell formatting in src/util/functions/dataExports/formatting.ts (formatValue, etc.) and field metadata from src/config/exportFieldDefinitions.ts.

Scope

Backend (attik-backend)

• Audit datetime serialization paths for CSV/XLSX (generateCSV.ts, generateXLSX.ts) so formatValue receives TZ context resolved from the exporting company.
• Sweep all datetime-like fields in exports—including linked-entity columns formatted post-join.

Frontend (attik-frontend)

• Preview/download UX should label or inherit TZ consistently if previews are shown client-side (src/app/tools/data-exports/).

References

• attik-backend/src/routes/dataExport.ts
• attik-backend/src/util/functions/dataExports/formatting.ts
• attik-backend/src/models/companySchema.ts