feat: display unlock conditions on all locked items

All locked items now show players exactly what they need to do next:
- Adventurers: "📜 Complete: [Quest Name]"
- Upgrades: "⚔️ Defeat: [Boss]" or "📜 Complete: [Quest]"
- Equipment (boss drops): "⚔️ Drop: [Boss Name]" instead of generic label
- Bosses: "⚔️ Defeat: [Previous Boss] first" or zone gate boss
- Quests: "📜 Complete: [Prerequisite Quest]"

Also wires adventurer unlocks through quests (militia through dragon_rider
had no unlock path), retroactively applies rewards on existing saves,
syncs boss reward arrays from defaults on load, and removes invalid
rune_stone reference from Forest Giant.

apps/api/src/data/bosses.ts

@@ -49,7 +49,7 @@ export const DEFAULT_BOSSES: Boss[] = [
     essenceReward: 400,
     crystalReward: 20,
     upgradeRewards: ["archmage_1"],
-    equipmentRewards: ["hide_armour", "rune_stone"],
+    equipmentRewards: ["hide_armour"],
     prestigeRequirement: 0,
     zoneId: "verdant_vale",
   },