feat(payments): remove EFT/havale, Stripe-only checkout + Turkish locale

EFT/Havale was retired; Stripe is now the sole payment method. Remove the
EFT code surface (shared PaymentMethod "eft" + EftPaymentInput + eftReceiptUrl,
EFT_RECEIPT_REQUIRED error code, billing UI receipt/filter/label paths,
payments.service eft read paths). DB columns (eft_receipt_url, bank_account_id,
bank_accounts) are kept and marked @deprecated to preserve historical records
and avoid a destructive migration — same pattern as the retired iyzico column.

Faz 3 conversion lever: set locale "tr" on the Stripe Checkout session. The
audience is Turkish B2B and ~60% of sessions reached the foreign-language
hosted page but never started a payment intent (pure abandonment, not decline).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/api/src/database/schema/core.ts

@@ -184,7 +184,9 @@ export const userBrands = pgTable(
   ],
 );
 
-// ─── Bank Accounts (EFT/Havale destination accounts, one active at a time) ────
+// ─── Bank Accounts ───────────────────────────────────
+// @deprecated EFT/Havale was retired (Stripe is the sole payment method). Table
+// kept only to preserve historical FK integrity; no rows are created anymore.
 export const bankAccounts = pgTable(
   "bank_accounts",
   {
@@ -225,7 +227,9 @@ export const payments = pgTable(
     iyzicoPaymentId: text("iyzico_payment_id"),
     stripeSessionId: text("stripe_session_id"),
     stripePaymentIntentId: text("stripe_payment_intent_id"),
+    /** @deprecated EFT/Havale retired (Stripe-only). Kept for historical data. */
     bankAccountId: uuid("bank_account_id").references(() => bankAccounts.id),
+    /** @deprecated EFT/Havale retired (Stripe-only). Kept for historical data. */
     eftReceiptUrl: text("eft_receipt_url"),
     adminNote: text("admin_note"),
     createdAt: timestamp("created_at", { withTimezone: true }).defaultNow().notNull(),