fix: Add required ASF policy links to site footer

The Johnzon website is failing 6 of 9 ASF website policy checks
(https://whimsy.apache.org/site/):

- Foundation link (in nav menu but not detected by scanner)
- Events (missing)
- License (missing)
- Security (existing link is broken - points to #)
- Copyright (missing)
- Privacy (pointed to project-level page)

This adds all required ASF policy links to the footer section of
site.xml, adds a copyright line, and updates the trademark text
("Apache feather logo" → "Apache logo").

See: https://www.apache.org/foundation/marks/pmcs
Checker: https://whimsy.apache.org/site/