fix(wallet-service): update init migration memo column to TEXT

Ensure new database installations use TEXT type for memo column from the start.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

backend/services/wallet-service/prisma/migrations/20241204000000_init/migration.sql

@@ -41,7 +41,7 @@ CREATE TABLE "wallet_ledger_entries" (
     "balance_after" DECIMAL(20,8),
     "ref_order_id" VARCHAR(100),
     "ref_tx_hash" VARCHAR(100),
-    "memo" VARCHAR(500),
+    "memo" TEXT,
     "payload_json" JSONB,
     "created_at" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,