Introduce the Strategy + Factory design: IItemUpdater (Name + Update),
an ItemUpdaterBase with the single shared [0,50] clamp helper, stateless
strategies for normal/Aged Brie/Sulfuras/Backstage, and a factory with
two-tier resolution (exact name via case-insensitive dictionary, then
Conjured prefix rule, then the default fallback).
Not wired into GildedRose yet; no behaviour change. The Conjured
strategy itself arrives in the feature commit.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
