feat: add insforge-test package

[pyramation]

Summary

New postgres/insforge-test package — an InsForge-optimized wrapper around pgsql-test, following the same pattern as supabase-test.

InsForge is structurally very similar to Supabase but less opinionated (no special admin user, standard PG port). The key role mapping differences:

INSFORGE_DEFAULTS = {
  roles: {
    anonymous: 'anon',
    authenticated: 'authenticated',
    administrator: 'project_admin',   // supabase: 'service_role'
    default: 'anon',
  },
  connections: {
    app: { user: 'postgres', ... }    // supabase: 'supabase_admin'
  }
};

INSFORGE_PG_DEFAULTS = {
  port: 5432,                          // supabase: 54322
  user: 'postgres',                    // supabase: 'supabase_admin'
};

Includes:

• getConnections() with InsForge defaults baked in (same merge precedence: defaults → env vars → user overrides)
• insertUser() helper for auth.users (identical to supabase-test — InsForge uses the same auth.users(id, email) pattern)
• Full re-exports from pgsql-test (snapshot utilities, seed adapters, etc.)
• README with InsForge-specific role docs, RLS testing examples, and a comparison table vs supabase-test

Link to Devin session: https://app.devin.ai/sessions/d1ba1a60226b4f6ea22409c44b0c9cc2
Requested by: @pyramation

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