Transmission #037: Achievements tab, toasts, and loot box queue (Step 5)

Step 5: Added ToastService (queued overlay toasts), extended ProgressionOrchestrator with PendingLootBoxes, TryClaimStatAchievement, ILootBoxNaming / HardcodedLootBoxNaming, and LootBoxInstance. Milestone unlocks call ToastService.TryShow with New Achievement '<title>'. InventoryPanelUI now has Items / Achievements / Boxes tabs (plus Grimoire when a grimoire exists), achievement rows with Claim, and a Boxes list populated after claim. PlayerStatTrackerProvider.OnEnable still adds the orchestrator. Edit Mode tests cover claim behavior. Implementation plan Step 5 is checked off.