make DocumentSection.title optional

src/core/domain/models.py

@@ -126,7 +126,7 @@ class DocumentSection(BaseModel):
         level: Header level (1-6 for h1-h6, 0 for Introduction)
         content: Section content with preserved Markdown formatting
     """
-    title: str = Field(..., min_length=1, description="Section title")
+    title: Optional[str] = Field(None, min_length=1, description="Section title")
     level: int = Field(..., ge=0, le=6, description="Header level (0=intro)")
     content: str = Field(..., description="Section content with formatting")
 
@@ -138,7 +138,9 @@ class DocumentSection(BaseModel):
     @classmethod
     def normalize_title(cls, value: str) -> str:
         """Normalize title by stripping whitespace."""
-        return value.strip()
+        if value:
+            return value.strip()
+        return value
 
     def is_introduction(self) -> bool:
         """Check if this is the introduction section."""

src/core/domain/parsers.py

@@ -57,7 +57,7 @@ def parse_markdown(text: str) -> List[DocumentSection]:
         if current_heading is not None or current_content_parts:
             content = "".join(current_content_parts).strip()
             if content:  # Only add sections with actual content
-                title = current_heading if current_heading else "Introduction"
+                title = current_heading
                 sections.append(
                     DocumentSection(
                         title=title,