Fix migration check: detect unmigrated data by checking data/customers.json

The previous check (directory existence) failed on production because
git pull created data/companies/ from committed config.json, causing
the migration to be skipped while customer data remained in data/ root.

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

api.php

@@ -120,18 +120,16 @@ function saveCompanyConfig(array $config): void {
 }
 
 function runMigration(): void {
-    // Tarkista onko migraatio jo tehty
     $companiesDir = DATA_DIR . '/companies';
-    if (file_exists($companiesDir) && is_dir($companiesDir)) return;
 
-    // Tarkista onko vanha data olemassa (pre-multitenant)
+    // Tarkista onko vanha data olemassa juuressa (pre-multitenant)
     $oldCustomers = DATA_DIR . '/customers.json';
-    if (!file_exists($oldCustomers)) return;
+    if (!file_exists($oldCustomers)) return; // Ei vanhaa dataa → ei migraatiota
 
-    // Luo yritykshakemisto
-    mkdir($companiesDir, 0755, true);
+    // Vanha data löytyy juuresta → siirretään yrityksen alle
+    if (!file_exists($companiesDir)) mkdir($companiesDir, 0755, true);
     $cuitunetDir = $companiesDir . '/cuitunet';
-    mkdir($cuitunetDir, 0755, true);
+    if (!file_exists($cuitunetDir)) mkdir($cuitunetDir, 0755, true);
 
     // Luo companies.json
     $companies = [[