[QA] Chat Reactions | Situational reaction particles render in front of avatar when camera is moved upward

### 🛠️ **Build version:**
`feat-chat-reactions-followup_6fd66b6b` (Unity 6000.4.0f1)

### 📔 **Issue Description:**

When observing another player sending situational reactions while moving the camera upward, the emoji particles render in front of the avatar instead of behind it. The spec states particles should always render behind nametags and bubbles. This appears related to the layer ordering issue previously fixed in #8298 / #8475, but triggered through camera movement rather than the original repro path.

### 👣 **STR:**

1. Log in with two separate instances (Player A and Player B)
2. As Player B, begin sending situational reactions repeatedly
3. As Player A, move close to Player B
4. While Player B is actively reacting, move Player A's camera upward

### ✔️ **Expected Result:**
Reaction particles render behind the avatar, nametag and bubbles at all camera angles, consistent with the design spec.

### ❌ **Actual Result with evidence:**
Reaction particles appear in front of the avatar when the camera is angled upward during an active reaction. Screenshots attached showing particles overlapping and rendering in front of the avatar across multiple frames.

https://github.com/user-attachments/assets/c335fe9f-9450-4148-a625-a1612840fd77

### ➗ **Reproduction:**

##### 🔁 Always - (note)

##### ⚠️ Intermittent - (note)
Reproduced when Player A moves camera upward while Player B is actively sending reactions. Not triggered under normal camera positioning. Requires two players in proximity.

##### ❓ Unknown - (note)

#### 🖥️ **Operative system and additional Notes:**

Low priority. Only visible when deliberately moving the camera upward during another player's reaction. Likely related to the billboard/layer sorting fix in #8298 — may share the same root cause but triggered by a different camera angle condition not covered by that fix.