Fixes + UX: combat HP, char delete, dice animation, compendium filters, import/export

- Combat: relabel HP controls Dmg/Heal, disabled at 0 (were silent no-ops)
- Characters: per-card Delete (confirm) + Export; header Import from JSON
- Dice: tumbling roll animation that settles on the result (a11y-safe)
- Compendium: per-category filters (monster type/CR, spell level/school, item rarity/type) + Clear
- Character import/export to portable JSON (reassigns id, validates on import)
- New: 4 io unit tests, e2e fixes spec (HP damage, delete, CR filter)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/features/combat/EncounterTracker.tsx

@@ -268,12 +268,12 @@ function CombatantRow({
             {c.hp.temp > 0 && <span className="text-info"> +{c.hp.temp}</span>}
           </div>
           <div className="mt-1 flex items-center gap-1">
-            <NumberField className="w-14" value={delta} min={0} onChange={setDelta} aria-label={`${c.name} HP change`} />
-            <Button size="sm" variant="danger" onClick={() => { onDamage(delta); setDelta(0); }}>
-              −
+            <NumberField className="w-14" value={delta} min={0} onChange={setDelta} aria-label={`${c.name} HP amount`} />
+            <Button size="sm" variant="danger" disabled={delta <= 0} onClick={() => { onDamage(delta); setDelta(0); }} title="Apply damage">
+              Dmg
             </Button>
-            <Button size="sm" variant="secondary" onClick={() => { onHeal(delta); setDelta(0); }}>
-              +
+            <Button size="sm" variant="secondary" disabled={delta <= 0} onClick={() => { onHeal(delta); setDelta(0); }} title="Heal">
+              Heal
             </Button>
           </div>
         </div>