fix: use quoted strings for size values in YAML to prevent time parsing

YAML parser interprets 16:9 as time format (16h 9m = 969s).
Using quoted strings "16:9" ensures correct string parsing.

tests/integration/test_rendering_flow.py

@@ -39,7 +39,7 @@ class TestRenderingFlow:
         """测试文本元素渲染"""
         yaml_content = """
 metadata:
-  size: 16:9
+  size: "16:9"
 
 slides:
   - elements:
@@ -81,7 +81,7 @@ slides:
         """测试图片元素渲染"""
         yaml_content = f"""
 metadata:
-  size: 16:9
+  size: "16:9"
 
 slides:
   - elements:
@@ -111,7 +111,7 @@ slides:
         """测试形状元素渲染"""
         yaml_content = """
 metadata:
-  size: 16:9
+  size: "16:9"
 
 slides:
   - elements:
@@ -145,7 +145,7 @@ slides:
         """测试表格元素渲染"""
         yaml_content = """
 metadata:
-  size: 16:9
+  size: "16:9"
 
 slides:
   - elements:
@@ -180,7 +180,7 @@ slides:
         """测试背景渲染"""
         yaml_content = """
 metadata:
-  size: 16:9
+  size: "16:9"
 
 slides:
   - background:
@@ -217,7 +217,7 @@ slides:
         """测试使用模板的幻灯片渲染"""
         yaml_content = f"""
 metadata:
-  size: 16:9
+  size: "16:9"
 
 slides:
   - template: title-slide
@@ -254,7 +254,7 @@ slides:
         """测试多张幻灯片渲染"""
         yaml_content = """
 metadata:
-  size: 16:9
+  size: "16:9"
 
 slides:
   - elements: