Row Level Security Policy Cookbook for Supabase

Create a "Supabase RLS Cookbook" repository with a docs site.
Core requirements:
1. Schema baseline migration: profiles, organisations, organisation_members (role enum: owner, admin, member, viewer), projects, documents, share_links.
2. One folder per pattern (owner-only, org membership, role-based write, public-read/private-write, share-by-link token, admin override via service role) with a migration containing the policies and a README explaining when to use it and common mistakes.
3. Storage policies for a private bucket keyed by organisation id and a public bucket for avatars.
4. pgTAP test files for each pattern that set the JWT claims for different users and assert allowed and denied selects, inserts, updates and deletes; all runnable with `supabase test db` against a local Supabase stack.
5. Docs site with one page per pattern, copy buttons, and a performance checklist (index policy columns, wrap auth.uid() in a select). Link to official docs instead of copying them.