Make API key and CORS settings per-company

- saatavuus endpoint finds company by API key, searches only that company
- config/config_update/generate_api_key now use company config
- API tab shows active company name
- Each company has own api_key and cors_origins in their config.json

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

index.html

@@ -437,7 +437,7 @@
         <div class="tab-content" id="tab-content-settings">
             <div class="main-container">
                 <div class="table-card" style="padding:1.5rem;">
-                    <h3 style="color:#0f3460;margin-bottom:1rem;border-bottom:2px solid #f0f2f5;padding-bottom:0.5rem;">Saatavuus-API</h3>
+                    <h3 style="color:#0f3460;margin-bottom:1rem;border-bottom:2px solid #f0f2f5;padding-bottom:0.5rem;"><span id="api-company-name"></span>Saatavuus-API</h3>
                     <p style="color:#666;font-size:0.85rem;margin-bottom:1rem;">Julkinen API jolla cuitunet.fi voi tarkistaa kuituverkon saatavuuden osoitteessa. Palauttaa vain osoite + nopeus - ei asiakastietoja.</p>
                     <div class="form-grid" style="max-width:600px;">
                         <div class="form-group full-width">