[TECH DEBT] AvatarRendering | must check if the wearable is no longer in the cache, otherwise ref count leaks

### 📊 **Priority Level:**
Low

### 📍 **Area/Component:**
`AvatarRendering\Thumbnails\Systems\ResolveAvatarAttachmentThumbnailSystem.cs`

### 📝 **Description:**
Unresolved TODO comment in the codebase:

> TODO must check if the wearable is no longer in the cache, otherwise ref count leaks

### 🔍 **Current State:**
The following line is present in `AvatarRendering\Thumbnails\Systems\ResolveAvatarAttachmentThumbnailSystem.cs`:

```csharp
/// TODO must check if the wearable is no longer in the cache, otherwise ref count leaks
```

### 💡 **Proposed Solution:**
Address the TODO as described in the comment, or remove it if no longer relevant.

### ⚖️ **Impact Assessment:**
#### Performance Impact:
To be assessed when the TODO is picked up.

#### Maintainability Impact:
Unresolved TODOs accumulate as tech debt and obscure the intended final state of the code.

#### Risk of Refactoring:
Low — scoped to the referenced location.

### 📈 **Effort Estimate:**
XS

### 🔗 **Dependencies:**
N/A

### 🖥️ **Additional Notes:**
Created automatically from a bulk TODO audit (todo-list.txt entry #6).

Start in AvatarRendering\Thumbnails\Systems\ResolveAvatarAttachmentThumbnailSystem.cs at the TODO and trace how wearables enter and leave the cache and how reference counts are updated. Confirm the behavior when a wearable is no longer cached, then verify that the reference count no longer leaks and remove the TODO once the behavior is addressed.

Written by the indexing model from the issue text.