Supabase Schema Plan

PROJECT CONTEXT:
I am building on Supabase and need a proper schema with relationships and row-level security.

GOAL:
Produce and apply a complete Supabase schema: tables, keys, RLS policies, and verified access rules.

REQUIREMENTS:
- Tables with correct types, keys, and relationships
- RLS enabled with policies per table
- Indexes for the query patterns
- Seed/verification queries proving the rules

CONSTRAINTS:
- Never leave RLS disabled on user data
- Policies must be tested from both allowed and denied perspectives

DEFINITION OF DONE:
- All tables created with relationships and constraints
- RLS policies enforce ownership correctly
- Denied access verifiably fails
- The app's queries work against the schema

COMMON FAILURES TO AVOID:
- RLS left off 'for now' and shipped that way
- Policies that allow everything (USING true) on private data
- Missing foreign keys causing orphaned rows
- Types chosen wrong (text for timestamps, no uuid defaults)