fix: fix return_rate_pct (ValueCell-ai#460)

## 📝 Pull Request Template

### 1. Related Issue
Closes # (issue number)

### 2. Type of Change (select one)
Type of Change: Bug Fix 

### 3. Description
Please describe the changes made and why they are necessary.

### 4. Testing
- [x] I have tested this locally.
- [x] I have updated or added relevant tests.

### 5. Checklist
- [x] I have read the [Code of Conduct](./CODE_OF_CONDUCT.md)
- [x] I have followed the [Contributing Guidelines](./CONTRIBUTING.md)
- [x] My changes follow the project's coding style

Author: su8su

python/valuecell/server/api/routers/strategy.py

@@ -204,7 +204,7 @@ def normalize_strategy_type(
         response_model=StrategyPerformanceResponse,
         summary="Get strategy performance and configuration overview",
         description=(
-            "Return ROI, model/provider, and final prompt strictly from templates (no fallback)."
+            "Return ROI strictly from portfolio view equity (total_value) relative to initial_capital; model/provider; and final prompt strictly from templates (no fallback)."
         ),
     )
     async def get_strategy_performance(

python/valuecell/server/services/strategy_service.py

@@ -219,19 +219,13 @@ async def get_strategy_performance(
             if snapshot
             else None
         )
-        pnl_value = (
-            StrategyService._combine_realized_unrealized(snapshot) if snapshot else None
-        )
 
         return_rate_pct: Optional[float] = None
         try:
-            if initial_capital and initial_capital > 0:
-                if total_value is not None:
-                    return_rate_pct = (
-                        (total_value - initial_capital) / initial_capital
-                    ) * 100.0
-                elif pnl_value is not None:
-                    return_rate_pct = (pnl_value / initial_capital) * 100.0
+            if initial_capital and initial_capital > 0 and total_value is not None:
+                return_rate_pct = (
+                    (total_value - initial_capital) / initial_capital
+                ) * 100.0
         except Exception:
             return_rate_pct = None