Fix SEO inconsistencies: founding year, accuracy rates, sitemap, alt text

- Fix founding year from 2018 to 2015 across about.php, organization-schema.php, and index.php schema
- Standardise data accuracy rate to 99.8% across about.php and services/web-scraping.php (was 99.7%/99.9%)
- Remove google-oauth-callback from sitemap.xml
- Fix UK Gambling Commission logo alt text (remove misleading 'regulatory compliance' label)

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

includes/schema/organization-schema.php

@@ -89,7 +89,7 @@ $organizationSchema = [
             'areaServed' => 'GB'
         ]
     ],
-    'foundingDate' => '2018',
+    'foundingDate' => '2015',
     'numberOfEmployees' => [
         '@type' => 'QuantitativeValue',
         'value' => '15'