fix: philosophers stone displays mana unit

components/PhilosophersStoneButton.vue

@@ -6,6 +6,7 @@
     :value="$store.state.mana"
     :current="current"
     :next="next"
+    unit="mana"
     @click="doAction"
   />
 </template>

components/ProgressButton.vue

@@ -30,6 +30,7 @@
       <span v-if="unit === 'apprenticeLevels'">L</span>{{ maxText }}
       <span v-if="unit === 'spareTime'" class="fas fa-hourglass-half" />
       <span v-if="unit === 'energy'" class="fas fa-bolt" />
+      <span v-if="unit === 'mana'" class="fas fa-star" />
     </span>
 
     <span