Restocking improvements

🐛 Bug Fix: Uncommon items are back on the shelves. Items in the uncommon rarity range (rarity 41–60) had quietly stopped showing up in NPC shops — Cinnamon Cream Coffee Cake, Cherry Candy Rocks, Mallarchy Care, and many others hadn't restocked in well over a month. The restocking system was processing rare tiers first (good), then commons (also good), but the way the budgets were set up meant common items always ate the leftover capacity before the uncommon pass ever ran. Each rarity tier now gets its own guaranteed slice of every shop's shelf space, so uncommons can't be crowded out. Common items still take whatever's left over, but they can't gobble up the whole shop anymore. Thanks to the players who flagged this.

🔍 Improvement: No more permanently-skipped items. Inside each rarity tier, the items that have gone the longest without being restocked now get picked first, instead of being chosen at random. Newly-added items (those that have never been restocked) jump to the front of the line. The end result: every item in a shop's catalog cycles through reliably rather than depending on luck, so nothing should ever drop off the shelves and be forgotten again.