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/20260202100000_add_award_ai_toggle/migration.sql

@@ -1,2 +1,4 @@
 -- AlterTable
-ALTER TABLE "SpecialAward" ADD COLUMN "useAiEligibility" BOOLEAN NOT NULL DEFAULT true;
+DO $$ BEGIN
+    ALTER TABLE "SpecialAward" ADD COLUMN "useAiEligibility" BOOLEAN NOT NULL DEFAULT true;
+EXCEPTION WHEN duplicate_column THEN NULL; END $$;