feat: extend notification system with batch sender, bulk dialog, and logging

Add NotificationLog schema extensions (nullable userId, email, roundId,
projectId, batchId fields), batch notification sender service, and bulk
notification dialog UI. Include utility scripts for debugging and seeding.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

prisma/migrations/20260304111008_extend_notification_log/migration.sql

@@ -0,0 +1,31 @@
+-- DropForeignKey
+ALTER TABLE "NotificationLog" DROP CONSTRAINT "NotificationLog_userId_fkey";
+
+-- AlterTable
+ALTER TABLE "NotificationLog" ADD COLUMN     "batchId" TEXT,
+ADD COLUMN     "email" TEXT,
+ADD COLUMN     "projectId" TEXT,
+ADD COLUMN     "roundId" TEXT,
+ALTER COLUMN "userId" DROP NOT NULL,
+ALTER COLUMN "channel" SET DEFAULT 'EMAIL';
+
+-- CreateIndex
+CREATE INDEX "NotificationLog_roundId_type_idx" ON "NotificationLog"("roundId", "type");
+
+-- CreateIndex
+CREATE INDEX "NotificationLog_projectId_idx" ON "NotificationLog"("projectId");
+
+-- CreateIndex
+CREATE INDEX "NotificationLog_batchId_idx" ON "NotificationLog"("batchId");
+
+-- CreateIndex
+CREATE INDEX "NotificationLog_email_idx" ON "NotificationLog"("email");
+
+-- AddForeignKey
+ALTER TABLE "NotificationLog" ADD CONSTRAINT "NotificationLog_userId_fkey" FOREIGN KEY ("userId") REFERENCES "User"("id") ON DELETE SET NULL ON UPDATE CASCADE;
+
+-- AddForeignKey
+ALTER TABLE "NotificationLog" ADD CONSTRAINT "NotificationLog_roundId_fkey" FOREIGN KEY ("roundId") REFERENCES "Round"("id") ON DELETE SET NULL ON UPDATE CASCADE;
+
+-- AddForeignKey
+ALTER TABLE "NotificationLog" ADD CONSTRAINT "NotificationLog_projectId_fkey" FOREIGN KEY ("projectId") REFERENCES "Project"("id") ON DELETE SET NULL ON UPDATE CASCADE;