Design a PostgreSQL-specific schema

# PostgreSQL Table Design 

## Use this skill when

- Designing a schema for PostgreSQL
- Selecting data types and constraints
- Planning indexes, partitions, or RLS policies
- Reviewing tables for scale and maintainability

## Do not use this skill when

- You are targeting a non-PostgreSQL database
- You only need query tuning without schema changes
- You require a DB-agnostic modeling guide

## Instructions

1. Capture entities, access patterns, and scale targets (rows, QPS, retention).
2. Choose data types and constraints that enforce invariants.
3. Add indexes for real query paths and validate with `EXPLAIN`.
4. Plan partitioning or RLS where required by scale or access control.
5. Review migration impact and apply changes safely.

## Safety