feat: sequential zone unlocking with dual boss+quest gate conditions

Zones now unlock in strict linear order. Each zone requires both the
final boss AND the final quest of the previous zone to be completed:

Verdant Vale → Shattered Ruins (forest_giant + ancient_ruins)
Shattered Ruins → Frozen Peaks (elder_dragon + dragon_lair)
Frozen Peaks → Shadow Marshes (void_titan + storm_citadel)
Shadow Marshes → Volcanic Depths (mud_kraken + plague_ruins)
Volcanic Depths → Astral Void (phoenix_lord + the_forge)

- Zone type gains `unlockQuestId` field alongside `unlockBossId`
- boss.ts checks both conditions before unlocking zone on boss defeat
- tick.ts checks both conditions and unlocks zones + first boss on
  quest completion if the boss condition is already met
- GameContext optimistic update also respects dual-condition logic
- BossPanel zone-gate hints now show both "⚔️ Defeat: X & 📜 Complete: Y"
- game.ts backfill syncs unlockQuestId and re-verifies zone status
  using both conditions, reverting incorrectly-unlocked saves

packages/types/src/interfaces/Zone.ts

@@ -6,6 +6,8 @@ export interface Zone {
   description: string;
   emoji: string;
   status: ZoneStatus;
-  /** Boss ID whose defeat unlocks this zone (null for the starter zone) */
+  /** Boss ID whose defeat is required to unlock this zone (null for the starter zone) */
   unlockBossId: string | null;
+  /** Quest ID that must be completed to unlock this zone (null for the starter zone) */
+  unlockQuestId: string | null;
 }