Convert read tracking to IPF & modernize cookie handling

[fiammybe]

Migrate forum/topic read tracking from Art to IPF and update cookie handling for PHP 8.x compatibility.

Checklist:

• Refactor Read, Readforum, Readtopic to IPF objects/handlers
• Extract all session/cookie or DB logic for read/unread state to a helper service
• Modernize all session/cookie code (e.g. use options arrays, httponly, etc.)
• Regression test: verify marking topics/forums read/unread still works in all modes
• Remove Art dependencies from read tracking