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_presentation.py

@@ -32,7 +32,7 @@ class TestTemplateCaching:
         # 创建使用模板的 YAML
         yaml_content = f"""
 metadata:
-  size: 16:9
+  size: "16:9"
 
 slides:
   - template: title-slide
@@ -69,7 +69,7 @@ class TestRenderSlide:
         """测试渲染使用模板的幻灯片"""
         yaml_content = f"""
 metadata:
-  size: 16:9
+  size: "16:9"
 
 slides:
   - template: title-slide
@@ -94,7 +94,7 @@ slides:
         # 有 subtitle 的情况
         yaml_with = f"""
 metadata:
-  size: 16:9
+  size: "16:9"
 
 slides:
   - template: title-slide
@@ -115,7 +115,7 @@ slides:
         # 没有 subtitle 的情况
         yaml_without = f"""
 metadata:
-  size: 16:9
+  size: "16:9"
 
 slides:
   - template: title-slide
@@ -136,7 +136,7 @@ slides:
         """测试变量传递"""
         yaml_content = f"""
 metadata:
-  size: 16:9
+  size: "16:9"
 
 slides:
   - template: title-slide
@@ -164,7 +164,7 @@ class TestPresentationWithoutTemplate:
         """测试直接渲染元素（不使用模板）"""
         yaml_content = """
 metadata:
-  size: 16:9
+  size: "16:9"
 
 slides:
   - elements: