feat: add YAML validation with check command and auto-validation

Implements comprehensive validation before PPTX conversion to catch errors early. Includes element-level validation (colors, fonts, table consistency) and system-level validation (geometry, resources). Supports standalone check command and automatic validation during conversion.

validators/result.py

@@ -0,0 +1,73 @@
+"""
+验证结果数据结构
+
+定义验证问题和验证结果的数据类。
+"""
+
+from dataclasses import dataclass, field
+from typing import List
+
+
+@dataclass
+class ValidationIssue:
+    """验证问题"""
+    level: str  # "ERROR" | "WARNING" | "INFO"
+    message: str
+    location: str  # "幻灯片 2, 元素 3"
+    code: str  # "ELEMENT_OUT_OF_BOUNDS"
+
+
+@dataclass
+class ValidationResult:
+    """验证结果"""
+    valid: bool  # 是否有 ERROR
+    errors: List[ValidationIssue] = field(default_factory=list)
+    warnings: List[ValidationIssue] = field(default_factory=list)
+    infos: List[ValidationIssue] = field(default_factory=list)
+
+    def has_errors(self) -> bool:
+        """是否有错误"""
+        return len(self.errors) > 0
+
+    def format_output(self) -> str:
+        """格式化为命令行输出"""
+        lines = []
+
+        lines.append("🔍 正在检查 YAML 文件...\n")
+
+        # 错误
+        if self.errors:
+            lines.append(f"❌ 错误 ({len(self.errors)}):")
+            for issue in self.errors:
+                location_str = f"[{issue.location}] " if issue.location else ""
+                lines.append(f"  {location_str}{issue.message}")
+            lines.append("")
+
+        # 警告
+        if self.warnings:
+            lines.append(f"⚠️  警告 ({len(self.warnings)}):")
+            for issue in self.warnings:
+                location_str = f"[{issue.location}] " if issue.location else ""
+                lines.append(f"  {location_str}{issue.message}")
+            lines.append("")
+
+        # 提示
+        if self.infos:
+            lines.append(f"ℹ️  提示 ({len(self.infos)}):")
+            for issue in self.infos:
+                location_str = f"[{issue.location}] " if issue.location else ""
+                lines.append(f"  {location_str}{issue.message}")
+            lines.append("")
+
+        # 总结
+        if not self.errors and not self.warnings and not self.infos:
+            lines.append("✅ 验证通过，未发现问题")
+        else:
+            summary_parts = []
+            if self.errors:
+                summary_parts.append(f"{len(self.errors)} 个错误")
+            if self.warnings:
+                summary_parts.append(f"{len(self.warnings)} 个警告")
+            lines.append(f"检查完成: 发现 {', '.join(summary_parts)}")
+
+        return "\n".join(lines)