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)

module/applications/spell-dialog.mjs

@@ -27,8 +27,10 @@ export default class OathHammerSpellDialog {
 
     const intRank      = actorSys.attributes.intelligence.rank
     const magicRank    = actorSys.skills.magic.rank
+    const magicMod     = actorSys.skills.magic.modifier ?? 0
     const magicColor   = actorSys.skills.magic.colorDiceType ?? "white"
-    const basePool     = intRank + magicRank
+    const basePool     = intRank + magicRank + magicMod
+    const magicModDisplay = magicMod > 0 ? `+${magicMod}` : magicMod < 0 ? `${magicMod}` : ""
 
     const currentStress   = actorSys.arcaneStress.value
     const stressThreshold = actorSys.arcaneStress.threshold
@@ -48,11 +50,12 @@ export default class OathHammerSpellDialog {
       { value: "black", label: game.i18n.localize("OATHHAMMER.ColorDice.Black"), selected: magicColor === "black" },
     ]
 
-    const enhancementOptions = Object.entries(SPELL_ENHANCEMENTS).map(([key, def]) => ({
-      value: key,
-      label: game.i18n.localize(def.label),
-      selected: key === "none",
-    }))
+    const enhancementOptions = Object.entries(SPELL_ENHANCEMENTS)
+      .filter(([key]) => key !== "none")
+      .map(([key, def]) => ({
+        value: key,
+        label: game.i18n.localize(def.label),
+      }))
 
     const bonusOptions = Array.from({ length: 13 }, (_, i) => {
       const v = i - 6
@@ -92,6 +95,8 @@ export default class OathHammerSpellDialog {
       element:       sys.element,
       intRank,
       magicRank,
+      magicMod,
+      magicModDisplay,
       basePool,
       poolSizeOptions,
       colorOptions,
@@ -132,16 +137,25 @@ export default class OathHammerSpellDialog {
 
     if (!result) return null
 
-    const enhKey = result.enhancement ?? "none"
-    const enh    = SPELL_ENHANCEMENTS[enhKey] ?? SPELL_ENHANCEMENTS.none
+    // Collect all checked enhancements and aggregate their effects
+    const selectedEnhs = Object.keys(SPELL_ENHANCEMENTS)
+      .filter(k => k !== "none" && result[`enh_${k}`] === "true")
+    const aggregated = selectedEnhs.reduce((acc, key) => {
+      const def = SPELL_ENHANCEMENTS[key]
+      acc.stress  += def.stress
+      acc.penalty += def.penalty
+      if (def.redDice)  acc.redDice  = true
+      if (def.noStress) acc.noStress = true
+      return acc
+    }, { stress: 0, penalty: 0, redDice: false, noStress: false })
 
     return {
       dv,
-      enhancement:     enhKey,
-      stressCost:      enh.stress,
-      poolPenalty:     enh.penalty,
-      redDice:         enh.redDice,
-      noStress:        enh.noStress,
+      enhancements:    selectedEnhs.length ? selectedEnhs : ["none"],
+      stressCost:      aggregated.stress,
+      poolPenalty:     aggregated.penalty,
+      redDice:         aggregated.redDice,
+      noStress:        aggregated.noStress,
       colorOverride:   result.colorOverride ?? magicColor,
       elementalBonus:  parseInt(result.elementalBonus) || 0,
       bonus:           parseInt(result.bonus)           || 0,