fix: scale tiers 11-16 upgrade costs and reorder arcane_scholar_1 (#113, #114)

Tiers 11-16 had essence costs of 150-2000 — far too low compared to
tier 10 (500K gold) and tier 17 (10M essence), creating a 5000x jump.

New costs scale ~5x per tier to bridge the gap:
  arcane_scholar_1 (tier 11): 150 → 1,000 essence
  shadow_assassin_1 (tier 12): 175 → 5,000 essence
  dark_templar_1 (tier 13): 200 → 25,000 essence
  void_walker_1 (tier 14): 300 → 100,000 essence
  celestial_guard_1 (tier 15): 750 → 500,000 essence
  divine_champion_1 (tier 16): 2,000 → 2,000,000 essence

Also reordered arcane_scholar_1 (tier 11) before shadow_assassin_1
(tier 12) to match ascending tier order in the file.

apps/api/src/data/upgrades.ts

@@ -297,23 +297,10 @@ export const defaultUpgrades: Array<Upgrade> = [
     target:     "adventurer",
     unlocked:   false,
   },
-  {
-    adventurerId: "shadow_assassin",
-    costCrystals: 0,
-    costEssence:  175,
-    costGold:     0,
-    description:  "Mastery of the shadow arts doubles assassin effectiveness.",
-    id:           "shadow_assassin_1",
-    multiplier:   2,
-    name:         "Shadow Arts",
-    purchased:    false,
-    target:       "adventurer",
-    unlocked:     false,
-  },
   {
     adventurerId: "arcane_scholar",
     costCrystals: 0,
-    costEssence:  150,
+    costEssence:  1000,
     costGold:     0,
     description:  "Access to forbidden libraries doubles scholar output.",
     id:           "arcane_scholar_1",
@@ -323,10 +310,23 @@ export const defaultUpgrades: Array<Upgrade> = [
     target:       "adventurer",
     unlocked:     false,
   },
+  {
+    adventurerId: "shadow_assassin",
+    costCrystals: 0,
+    costEssence:  5000,
+    costGold:     0,
+    description:  "Mastery of the shadow arts doubles assassin effectiveness.",
+    id:           "shadow_assassin_1",
+    multiplier:   2,
+    name:         "Shadow Arts",
+    purchased:    false,
+    target:       "adventurer",
+    unlocked:     false,
+  },
   {
     adventurerId: "dark_templar",
     costCrystals: 0,
-    costEssence:  200,
+    costEssence:  25_000,
     costGold:     0,
     description:
       "A sworn oath to the darkness of the marshes doubles templar output.",
@@ -340,7 +340,7 @@ export const defaultUpgrades: Array<Upgrade> = [
   {
     adventurerId: "void_walker",
     costCrystals: 0,
-    costEssence:  300,
+    costEssence:  100_000,
     costGold:     0,
     description:
       "Walking through the void itself doubles the output of your void walkers.",
@@ -354,7 +354,7 @@ export const defaultUpgrades: Array<Upgrade> = [
   {
     adventurerId: "celestial_guard",
     costCrystals: 0,
-    costEssence:  750,
+    costEssence:  500_000,
     costGold:     0,
     description:
       "A blessing from the celestials themselves doubles guard output.",
@@ -368,7 +368,7 @@ export const defaultUpgrades: Array<Upgrade> = [
   {
     adventurerId: "divine_champion",
     costCrystals: 0,
-    costEssence:  2000,
+    costEssence:  2_000_000,
     costGold:     0,
     description:  "An unbreakable oath to the divine doubles champion output.",
     id:           "divine_champion_1",