feat: luck bonus, inventory slots bonus, multi-enhancements, magic skill modifier

- Add luck.bonus field to character DataModel; included in prepareDerivedData
   (luck.max = fate.rank + bonus); shown as editable +bonus field next to
   luck max in edit mode (same UX as grit bonus)

 - Add inventory.slotsBonus field to character DataModel; Equipment tab now
   shows an editable "Bonus Slots" input that adds to the calculated max slots
   (10 + Might×2 + bonus)

 - Replace single Enhancement <select> in spell cast dialog with a checkbox
   list; multiple enhancements can now be selected simultaneously — stress
   costs, pool penalties, and boolean flags (redDice, noStress) are aggregated
   across all active enhancements

 - Include skills.magic.modifier in basePool for both spell and miracle dialogs
   and in baseDice in rollSpellCast / rollMiracleCast; modifier is shown in
   the dialog pool-info line and in the chat card when non-zero

 - Fix: pool-reduction indicator in rollSpellCast now compares against
   intRank + magicRank + magicMod (was missing magicMod)

less/roll-dialog.less

@@ -553,10 +553,47 @@
     i { flex-shrink: 0; }
   }
 
-  // Wide select for enhancement list
+  // Wide select for enhancement list (legacy, kept for miracle dialog)
   select.enhancement-select {
     min-width: 220px;
   }
+
+  // Multi-enhancement checkbox list
+  .roll-option-enhancements {
+    align-items: flex-start;
+
+    .enhancements-header {
+      padding-top: 3px;
+      flex-shrink: 0;
+    }
+
+    .enhancements-list {
+      display: flex;
+      flex-direction: column;
+      gap: 4px;
+    }
+
+    .enhancement-item {
+      display: flex;
+      align-items: center;
+      gap: 6px;
+
+      input[type="checkbox"] {
+        flex-shrink: 0;
+        width: 14px;
+        height: 14px;
+        cursor: pointer;
+      }
+
+      .enh-name {
+        font-size: @font-size-sm;
+        color: @color-dark;
+        cursor: pointer;
+        margin: 0;
+        font-weight: normal;
+      }
+    }
+  }
 }
 
 // Chat card additions for spell/miracle