server: schema — City map coords, Mission narrative/level/loot fields

Add mapX/mapY to City for SVG map positioning; add description,
minLevel, rewardItemId/Quantity to Mission; add named relations
MissionRequiredItem and MissionRewardItem on Item. Seed updated
with Italian city coordinates.

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

server/prisma/migrations/20260609220134_game_improvements/migration.sql

@@ -0,0 +1,12 @@
+-- AlterTable
+ALTER TABLE "City" ADD COLUMN     "mapX" DOUBLE PRECISION NOT NULL DEFAULT 50,
+ADD COLUMN     "mapY" DOUBLE PRECISION NOT NULL DEFAULT 50;
+
+-- AlterTable
+ALTER TABLE "Mission" ADD COLUMN     "description" TEXT NOT NULL DEFAULT '',
+ADD COLUMN     "minLevel" INTEGER NOT NULL DEFAULT 1,
+ADD COLUMN     "rewardItemId" TEXT,
+ADD COLUMN     "rewardItemQuantity" INTEGER;
+
+-- AddForeignKey
+ALTER TABLE "Mission" ADD CONSTRAINT "Mission_rewardItemId_fkey" FOREIGN KEY ("rewardItemId") REFERENCES "Item"("id") ON DELETE SET NULL ON UPDATE CASCADE;