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)

templates/spell-cast-dialog.hbs

@@ -31,6 +31,7 @@
     <div class="pool-info-line">
       {{localize "OATHHAMMER.Skill.Magic"}} ({{localize "OATHHAMMER.Attribute.Intelligence"}} {{intRank}})
       + {{localize "OATHHAMMER.Label.SkillRank"}} {{magicRank}}
+      {{#if magicModDisplay}} {{localize "OATHHAMMER.Label.SkillModifier"}} {{magicModDisplay}}{{/if}}
       = <strong>{{basePool}}d6</strong>
     </div>
 
@@ -52,11 +53,16 @@
       <span class="roll-option-hint">{{localize "OATHHAMMER.Dialog.DiceColorHint"}}</span>
     </div>
 
-    <div class="roll-option-row">
-      <label>{{localize "OATHHAMMER.Dialog.Enhancement"}}</label>
-      <select name="enhancement" class="enhancement-select">
-        {{#each enhancementOptions}}<option value="{{value}}"{{#if selected}} selected{{/if}}>{{label}}</option>{{/each}}
-      </select>
+    <div class="roll-option-row roll-option-enhancements">
+      <label class="enhancements-header">{{localize "OATHHAMMER.Dialog.Enhancement"}}</label>
+      <div class="enhancements-list">
+        {{#each enhancementOptions}}
+        <div class="enhancement-item">
+          <input type="checkbox" id="enh_{{value}}" name="enh_{{value}}" value="true">
+          <label for="enh_{{value}}" class="enh-name">{{label}}</label>
+        </div>
+        {{/each}}
+      </div>
     </div>
 
     {{#if isElemental}}