chore(db): finish Prisma cutover to Drizzle Kit tooling

Move CMS SQL to drizzle/migrations, drop prisma packages/schema, wire drizzle-kit scripts, and regenerate schema names from src/db/schema.ts.

Co-authored-by: Cursor <[email protected]>

drizzle/migrations/0008_add_bans_user_id_index.sql

@@ -0,0 +1,4 @@
+-- 0008_add_bans_user_id_index.sql
+-- Adds an index on bans.user_id to speed up ban lookups by user (used by
+-- the access guard on every page request for logged-in users).
+CREATE INDEX IF NOT EXISTS `bans_user_id_index` ON `bans` (`user_id`);