feat: Remove banned mana types (life, blood, wood, mental, force) and lifesteal

- Remove life, blood, wood, mental, force mana types from ELEMENTS
- Remove all spells using banned mana types
- Remove lifesteal from all remaining spells and effects
- Update guardian perks to remove lifesteal mentions
- Remove research skills for banned spell types
- Update tests to reflect new element structure
- Add BANNED CONTENT section to AGENTS.md (lifesteal/healing ban)
- Add mana types overview to README.md and AGENTS.md
- All 44 tests pass, lint clean

src/lib/game/store.ts

@@ -1086,13 +1086,6 @@ export const useGameStore = create<GameStore>()(
                   log = [`✨ Spell Echo! Double damage!`, ...log.slice(0, 49)];
                 }
                 
-                // Lifesteal effect
-                const lifestealEffect = spellDef.effects?.find(e => e.type === 'lifesteal');
-                if (lifestealEffect) {
-                  const healAmount = dmg * lifestealEffect.value;
-                  rawMana = Math.min(rawMana + healAmount, maxMana);
-                }
-                
                 // Apply damage to enemy
                 enemy.hp = Math.max(0, enemy.hp - Math.floor(dmg));
               }