feat: add Soroban WAL and crash recovery foundation

prisma/schema/migrations/20260830000000_add_soroban_wal/migration.sql

@@ -0,0 +1,29 @@
+CREATE TYPE "SorobanWALOperation" AS ENUM ('buy', 'sell');
+CREATE TYPE "SorobanWALState" AS ENUM ('PENDING', 'SUBMITTED', 'CONFIRMED', 'FAILED', 'ROLLED_BACK');
+
+CREATE TABLE "soroban_wal_entries" (
+    "id" TEXT NOT NULL,
+    "idempotencyKey" TEXT NOT NULL,
+    "operation" "SorobanWALOperation" NOT NULL,
+    "wallet" TEXT NOT NULL,
+    "creatorWallet" TEXT NOT NULL,
+    "amount" DECIMAL(65,30) NOT NULL,
+    "expectedSupplyBefore" DECIMAL(65,30) NOT NULL,
+    "xdrPayload" TEXT NOT NULL,
+    "state" "SorobanWALState" NOT NULL DEFAULT 'PENDING',
+    "txHash" TEXT,
+    "submittedAt" TIMESTAMP(3),
+    "confirmedAt" TIMESTAMP(3),
+    "error" TEXT,
+    "createdAt" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    "updatedAt" TIMESTAMP(3) NOT NULL,
+
+    CONSTRAINT "soroban_wal_entries_pkey" PRIMARY KEY ("id")
+);
+
+CREATE UNIQUE INDEX "soroban_wal_entries_idempotencyKey_key"
+    ON "soroban_wal_entries"("idempotencyKey");
+CREATE UNIQUE INDEX "soroban_wal_entries_txHash_key"
+    ON "soroban_wal_entries"("txHash");
+CREATE INDEX "soroban_wal_entries_state_createdAt_idx"
+    ON "soroban_wal_entries"("state", "createdAt");

prisma/schema/soroban-wal.prisma

@@ -0,0 +1,33 @@
+enum SorobanWALOperation {
+  BUY  @map("buy")
+  SELL @map("sell")
+}
+
+enum SorobanWALState {
+  PENDING
+  SUBMITTED
+  CONFIRMED
+  FAILED
+  ROLLED_BACK
+}
+
+model SorobanWALEntry {
+  id                   String              @id @default(cuid())
+  idempotencyKey       String              @unique
+  operation            SorobanWALOperation
+  wallet               String
+  creatorWallet        String
+  amount               Decimal
+  expectedSupplyBefore Decimal
+  xdrPayload           String              @db.Text
+  state                SorobanWALState     @default(PENDING)
+  txHash               String?             @unique
+  submittedAt          DateTime?
+  confirmedAt          DateTime?
+  error                String?             @db.Text
+  createdAt            DateTime            @default(now())
+  updatedAt            DateTime            @updatedAt
+
+  @@index([state, createdAt])
+  @@map("soroban_wal_entries")
+}