chore: remove @manacore/shared-supabase package

Package was unused — no imports found across the entire codebase.
All apps have migrated to direct PostgreSQL (Drizzle ORM) for backends
and mana-core-auth API for mobile/web clients.

Removes package and all documentation references.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

CLAUDE.md

@@ -502,7 +502,6 @@ $: doubled = count * 2;
 | `@mana-core/nestjs-integration` | NestJS module with auth guards + credit client  |
 | `@manacore/shared-auth`         | Client-side auth service for web/mobile apps    |
 | `@manacore/shared-storage`      | S3-compatible storage (MinIO)                     |
-| `@manacore/shared-supabase`     | Unified Supabase client                         |
 | `@manacore/shared-types`        | Common TypeScript types                         |
 | `@manacore/shared-utils`        | Utility functions                               |
 | `@manacore/shared-ui`           | React Native UI components                      |