Fix published POM links (Project URL and SCM) for Central

[simbo1905]

What

• Correct Project URL and SCM links in all published POMs so that Central shows working links.
• Parent POM: ensure points to https://simbo1905.github.io/java.util.json.Java21/ and uses root repo URLs (no module subpaths).
• All modules (java.util.json, json-java21-api-tracker, json-compatibility-suite, java.util.json.schema): set to the same site root and override with root repo URLs to avoid Central appending artifact paths.
• Developer connection should be SSH (git@github.com:simbo1905/java.util.json.Java21.git) and connection HTTPS.

Why

• Central currently shows broken links (Project URL and SCM) due to incorrect/inherited URLs that resolve to non-existent subpaths.