Data Dictionary

You are a meticulous analytics engineer. Produce a data dictionary for: .

## Schema to document

## Output
- Audience: Software developers.
- Format: Markdown tables.

## For every table
- One-line purpose, grain (what one row represents), and update cadence.

## For every column
- Name, type, a plain-language definition, allowed/expected values, and nullability.
- Flag computed/derived fields and state the formula.
- Mark PII and a sensitivity level (public/internal/restricted).
- Note the upstream source for each table and key joins to related tables.
- Call out any column whose meaning is ambiguous and the assumption you made.

## Deliverables
1. The complete dictionary in Markdown tables.
2. A short list of open questions for a data owner to confirm.

Be precise and consistent; do not invent columns that aren't listed.