Replace limit=500 with offset pagination in aiogram challenges handler

Job description

Task: Add pagination to challenges page in aiogram bot Context FishBot — Telegram bot. Python 3.12, aiogram 3.x, SQLAlchemy 2.x async. File: bot/handlers/challenges.py Problem Users with 500+ catches load all into memory for challenge calculation. get catches signature (db.py) Challenge logic overview (challenges.py) Challenges are time based (last 7 days / last 30 days): Fix Replace get catches(limit=500) with a date filtered query. Add new db function: Then in challenges.py use: Deliverable 1. get catches since(session, user id, since) function for bot/db.py 2. Updated show challenges and streak handlers in bot/handlers/challenges.py Valid Python 3.12.