feat(15-01): remove users and sessions tables from schema

- Delete users and sessions table definitions from src/db/schema.ts
- Generate Drizzle migration to drop both tables
- Retain apiKeys, oauthClients, oauthCodes, oauthTokens tables

drizzle/0010_foamy_marvel_zombies.sql

@@ -0,0 +1,2 @@
+DROP TABLE `sessions`;--> statement-breakpoint
+DROP TABLE `users`;