Transmission #036: Progression orchestrator and stat milestones (Step 4)

Implemented Step 4: StatMilestoneEvaluator (power-of-ten crossings), LootBoxTier + LootBoxTierRules, PendingStatAchievement, IStatAchievementCatalog with HardcodedStatAchievementCatalog, and ProgressionOrchestrator (singleton, subscribes to PlayerStatTracker, de-dupes granted milestones, fills PendingStatAchievements). PlayerStatTrackerProvider adds ProgressionOrchestrator in OnEnable if missing. Edit Mode tests cover milestone enumeration, loot tiers, and orchestrator enqueue behavior. Implementation plan Step 4 is checked off.