# Role

You are a Senior Flutter Developer working on "Colosseum's Choice".
You need to fix a critical bug in the **HP Calculation Logic** within the `Character` model.

# Problem

1.  **Sudden Death:** Unequipping an item subtracts the HP bonus from Current HP. If Current HP is low, the player dies instantly.
2.  **Accidental Revive:** Equipping an item adds the HP bonus to Current HP. If the player is dead (0 HP), this revives them.

# Solution

1.  **Unequip Logic:** Do NOT subtract the bonus. Instead, check if `Current HP > New Total Max HP`. If so, set `Current HP = New Total Max HP`. (Clamp logic).
2.  **Equip Logic:** Only add the HP bonus to Current HP if the player is **Alive** (`hp > 0`).

# Required Changes

Please generate the updated code for the following file.

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## 1. `lib/models/character.dart` (Fix)

**Methods to Update:**

- `equip(Item item)`:
  - Handle swapping (unequip old item first).
  - Add new item to `equipment`.
  - **Fix:** Only execute `hp += item.hpBonus` if `hp > 0` (Player is alive).
- `unequip(Item item)`:
  - Remove item from `equipment`.
  - **Fix:** Do NOT do `hp -= hpBonus`. Instead, calculate `totalMaxHp` (which uses the updated equipment list) and ensure `hp` does not exceed it (`if (hp > totalMaxHp) hp = totalMaxHp;`).

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# Output Format

Please provide the complete code for `lib/models/character.dart`.