Remove drizzle-kit dependency (#806)

- Remove drizzle-kit from dependencies
- Remove db:generate, db:push, db:studio scripts from package.json
- Delete drizzle.config.ts (only used by drizzle-kit)
- Delete drizzle-kit snapshot file (migrations/meta/0048_tags_updated_at_snapshot.json)
- Update comments in migration runner and SQL files to remove drizzle-kit references

The custom migration runner (scripts/run-migrations.ts) and journal format
(migrations/meta/_journal.json) are unaffected. drizzle-orm is retained.

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

Author: claude

drizzle.config.ts

@@ -1,4 +1,4 @@
-- We use a custom migration tool, not drizzle-kit. Never run migrations with drizzle-kit, always use `pnpm db:migrate` or `pnpm db:migrate:test`. See ../scripts/migrate.ts if you need details.
+- We use a custom migration runner, not drizzle-kit. The migration format looks like drizzle-kit's but drizzle-kit is not installed. Never run migrations with drizzle-kit, always use `pnpm db:migrate` or `pnpm db:migrate:test`. See ../scripts/migrate.ts if you need details.
 - Always add new migrations to meta/\_journal.json. Only migrations in the journal will be run.
 - Test new migrations using `pnpm test:integration`
 - Read @schema.sql and keep it up to date with `pnpm db:schema`