Make migrations idempotent and add missing tables

- Make all pending migrations idempotent (safe to re-run)
- Disable decouple_projects_from_rounds migration (schema not changed)
- Add ProjectTag table for AI tagging
- Add AssignmentJob table for AI assignment progress

On server deployment, run: npx prisma migrate deploy

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

prisma/migrations/20260204000000_add_round_entry_notification/migration.sql

@@ -1,4 +1,6 @@
 -- AddRoundEntryNotification
 -- Adds the entryNotificationType column to Round table for configurable notifications
 
-ALTER TABLE "Round" ADD COLUMN "entryNotificationType" TEXT;
+DO $$ BEGIN
+    ALTER TABLE "Round" ADD COLUMN "entryNotificationType" TEXT;
+EXCEPTION WHEN duplicate_column THEN NULL; END $$;