Remove impossible mechanics and fix game balance

- Remove lifesteal from spells (player has no health to heal)
- Remove execute effects (too powerful instant-kill mechanic)
- Remove freeze status effect (doesn't fit game design)
- Remove knowledgeRetention skill (study progress is now always saved)
- Fix soulBinding skill (now binds guardian essence to equipment)
- Buff ancientEcho skill (+1 capacity per level instead of per 2 levels)
- Rename lifesteal_5 to mana_siphon_5 in enchantment effects
- Update guardian perks:
  - Water: 10% double cast chance instead of lifesteal
  - Dark: 25% crit chance instead of lifesteal
  - Life: 30% damage restored as mana instead of healing
  - Death: +50% damage to enemies below 50% HP instead of execute
- Add floor armor system (flat damage reduction)
- Update spell effects display in UI
- Fix study cancellation - progress is always saved when pausing

src/components/game/tabs/SpireTab.tsx

@@ -380,9 +380,10 @@ export function SpireTab({ store }: SpireTabProps) {
                         <div className="flex gap-1 flex-wrap mt-1">
                           {spellDef.effects.map((eff, i) => (
                             <Badge key={i} variant="outline" className="text-xs py-0">
-                              {eff.type === 'lifesteal' && `🩸 ${Math.round(eff.value * 100)}%`}
                               {eff.type === 'burn' && `🔥 Burn`}
-                              {eff.type === 'freeze' && `❄️ Freeze`}
+                              {eff.type === 'stun' && `⚡ Stun`}
+                              {eff.type === 'pierce' && `🎯 Pierce`}
+                              {eff.type === 'multicast' && `✨ Multicast`}
                             </Badge>
                           ))}
                         </div>