fix(paytr): encode hyphens in tenantId as Z in merchantOid

PayTR rejects merchant_oid with non-alphanumeric chars. Real Appwrite
tenant IDs are hex (a-z0-9) and safe, but demo-tenant-001 contains
hyphens. Encode - as Z (never appears in Appwrite hex IDs) in the
merchantOid; decode back in the callback.

src/lib/appwrite/subscription-actions.ts

@@ -213,9 +213,10 @@ export async function getPayTRTokenAction(formData: FormData): Promise<string> {
 
   const timestamp = Date.now().toString();
   const random = Math.random().toString(36).slice(2, 8);
-  // Uppercase harfler separator — tenantId (lowercase a-z0-9) hiçbir zaman içermez
-  // Format: {tenantId}T{timestamp}{random}P{plan}X{period}
-  const merchantOid = `${ctx.tenantId}T${timestamp}${random}P${planId}X${period}`;
+  // Hyphens encoded as Z (Appwrite hex IDs never contain uppercase letters)
+  // Format: {encodedTenantId}T{timestamp}{random}P{plan}X{period}
+  const encodedTenantId = ctx.tenantId.replace(/-/g, "Z");
+  const merchantOid = `${encodedTenantId}T${timestamp}${random}P${planId}X${period}`;
 
   const discountLabel = discountCodeRaw ? ` + ${discountCodeRaw.toUpperCase()} İndirimi` : "";
   const userBasket: Array<[string, string, number]> = [