refactor(db): replace sqlc with handwritten pgx repos

- Finish Paddle-to-Stripe billing migration; drop paddle/stripe libs
- Renumber migrations; add 00012 memberships+manage_token,
  00013 location_type_capacity
- Add tests: admin, auth, bookings customer service
- Remove graphify-out artifacts and stale env files

Authored By: TDvorak <[email protected]>

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

apps/backend/migrations/00006_neon_auth_subjects.sql

@@ -0,0 +1,18 @@
+-- +goose Up
+ALTER TABLE users
+  ADD COLUMN IF NOT EXISTS neon_subject text;
+
+CREATE UNIQUE INDEX IF NOT EXISTS idx_users_neon_subject
+  ON users (neon_subject)
+  WHERE neon_subject IS NOT NULL;
+
+UPDATE users
+SET neon_subject = 'demo-owner',
+    updated_at = now()
+WHERE email = '[email protected]'
+  AND neon_subject IS NULL;
+
+-- +goose Down
+DROP INDEX IF EXISTS idx_users_neon_subject;
+ALTER TABLE users
+  DROP COLUMN IF EXISTS neon_subject;