sandbox phase 1: schema + seed (sandbox_sis, upload_events)

[William-Hill]

Parent: #116 · Spec: docs/superpowers/specs/2026-05-02-sis-pdp-ar-sandbox-design.md

Scope

• New sandbox_sis Postgres schema with Banner-flavored tables: students, enrollments, terms, courses, grades, financial_aid, holds.
• New upload_events table (append-only) keyed by event_id with source/target stage, row count, transformations, actor, ts.
• sandbox/seed_sis.py deterministic seed (~500 students) matching Bishop State distributions, no real identifiers.
• is_sandbox=true flag and namespacing rules so sandbox data is wipeable in one command.

Acceptance

• Migration creates sandbox_sis and upload_events
• python sandbox/seed_sis.py --seed 42 produces identical output across runs
• make sandbox-reset drops only sandbox data, leaves real tables untouched

Estimate: 2–3 days.