fix: use arcane spell defense D30 chart for spell saves

Bug: saveSpell local var initialized to false (line 142), while
dialog checkbox was pre-checked via dialogContext.saveSpell =
game.lethalFantasy.spellDefense.  If user didn't click the checkbox,
D30 call used SAVING_THROWS chart instead of ARCANE_SPELL_DEFENSE.

Also: game.lethalFantasy.spellDefense was set true before spell
defense rolls but never cleared, leaking to subsequent non-spell saves.

Fix: initialize saveSpell from the one-shot flag and delete it
immediately.  Dialog context now uses the local saveSpell variable
instead of re-reading the deleted flag.

module/documents/roll.mjs

@@ -139,7 +139,9 @@ export default class LethalFantasyRoll extends Roll {
     let hasGrantedDice = false
     let pointBlank = false
     let letItFly = false
-    let saveSpell = false
+    let saveSpell = game.lethalFantasy?.spellDefense ?? false
+    // Consume one-shot flag so it doesn't leak to subsequent non-spell saves
+    if (game.lethalFantasy) delete game.lethalFantasy.spellDefense
     let beyondSkill = false
     let hasStaticModifier = false
     let hasExplode = true
@@ -358,7 +360,7 @@ export default class LethalFantasyRoll extends Roll {
       dice,
       hasTarget: options.hasTarget,
       modifier,
-      saveSpell: game.lethalFantasy?.spellDefense ?? false,
+      saveSpell,
       favor: "none",
       targetName,
       isRangedAttack