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

AGENTS.md

@@ -365,3 +365,67 @@ const useGameStore = create<GameStore>()(
 - Extract computed stats and utility functions to `computed-stats.ts` when >50 lines
 - Use barrel exports (`index.ts`) for clean imports
 - Follow the slice pattern for store organization (see below)
+
+---
+
+## 🚫 BANNED CONTENT - NEVER ADD THESE
+
+### Lifesteal and Healing are BANNED
+**DO NOT add lifesteal or healing mechanics to player abilities.**
+
+This includes:
+- `lifesteal` spell effects
+- `heal` or `regeneration` abilities for the player
+- Any mechanic that restores player HP or mana based on damage dealt
+- Life-stealing weapons or enchantments
+
+**Rationale**: The game's core design is that the player cannot take damage - only floors can. Healing/lifesteal mechanics are unnecessary and would create confusing gameplay.
+
+### Banned Mana Types
+The following mana types have been **removed** and should **never be re-added**:
+- `life` - Healing/lifesteal themed (banned)
+- `blood` - Life + Water compound (banned due to lifesteal theme)
+- `wood` - Life + Earth compound (banned due to life connection)
+- `mental` - Mind/psionic themed (removed for design consistency)
+- `force` - Telekinetic themed (removed for design consistency)
+
+---
+
+## 🔮 Mana Types Overview
+
+### Base Mana Types (7)
+| Element | Symbol | Color | Theme |
+|---------|--------|-------|-------|
+| Fire | 🔥 | #FF6B35 | Destruction, burn damage |
+| Water | 💧 | #4ECDC4 | Flow, freeze effects |
+| Air | 🌬️ | #00D4FF | Speed, wind damage |
+| Earth | ⛰️ | #F4A261 | Stability, armor pierce |
+| Light | ☀️ | #FFD700 | Radiance, holy damage |
+| Dark | 🌑 | #9B59B6 | Shadows, void damage |
+| Death | 💀 | #778CA3 | Decay, rot damage |
+
+### Utility Mana Types (1)
+| Element | Symbol | Color | Theme |
+|---------|--------|-------|-------|
+| Transference | 🔗 | #1ABC9C | Mana transfer, Enchanter attunement |
+
+### Compound Mana Types (3)
+| Element | Recipe | Theme |
+|---------|--------|-------|
+| Metal | Fire + Earth | Armor piercing, forged weapons |
+| Sand | Earth + Water | AOE damage, desert winds |
+| Lightning | Fire + Air | Fast damage, armor pierce, chain effects |
+
+### Exotic Mana Types (3)
+| Element | Recipe | Theme |
+|---------|--------|-------|
+| Crystal | Sand + Sand + Light | Prismatic, high damage |
+| Stellar | Fire + Fire + Light | Cosmic, ultimate fire/light |
+| Void | Dark + Dark + Death | Oblivion, ultimate dark/death |
+
+### Mana Type Hierarchy
+```
+Base Elements (7) → Compound (3) → Exotic (3)
+                      ↓
+              Utility (1) ← Special attunement-based
+```