fix: resolve critical PDF generation bugs

Fixed two critical errors preventing PDF downloads:

1. KeyError: "Style 'BodyText' already defined in stylesheet"
   - Renamed custom style from "BodyText" to "ReportBodyText"
   - BodyText is a reserved ReportLab built-in style name
   - Updated all references to use new name

2. AttributeError: 'int' object has no attribute 'encode'
   - StreamingResponse expected an iterator, not BytesIO directly
   - Added iterfile() generator function to yield BytesIO chunks
   - Properly resets buffer position with seek(0) before iteration

Additional:
- Removed unused hex_to_rgb_tuple() function (dead code cleanup)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/backend/core/pdf_service.py

@@ -38,12 +38,6 @@ NEUTRAL_100 = colors.HexColor("#F3F4F6")
 WHITE = colors.white
 
 
-def hex_to_rgb_tuple(hex_color: str) -> tuple[float, float, float]:
-    """Convert hex color to RGB tuple (0-1 range)"""
-    hex_color = hex_color.lstrip("#")
-    return tuple(int(hex_color[i : i + 2], 16) / 255 for i in (0, 2, 4))
-
-
 def compute_content_hash(analysis: SwotAnalysis) -> str:
     """
     Compute SHA-256 hash of SWOT analysis content for caching.
@@ -124,7 +118,7 @@ class SwotPDFGenerator:
         # Body text style
         self.styles.add(
             ParagraphStyle(
-                name="BodyText",
+                name="ReportBodyText",
                 parent=self.styles["Normal"],
                 fontSize=11,
                 textColor=NEUTRAL_700,
@@ -243,7 +237,7 @@ class SwotPDFGenerator:
 
         # Wrap summary in a table for better styling
         summary_para = Paragraph(
-            self.analysis.analysis, self.styles["BodyText"]
+            self.analysis.analysis, self.styles["ReportBodyText"]
         )
         summary_table = Table([[summary_para]], colWidths=[6.5 * inch])
         summary_table.setStyle(

src/backend/site/router.py

@@ -227,9 +227,13 @@ async def download_pdf(request: Request) -> StreamingResponse:
     # Prepare filename
     filename = f"swot-analysis-{session_id[:8]}.pdf"
 
-    # Return as streaming response
+    # Return as streaming response (iterate over BytesIO in chunks)
+    def iterfile():
+        pdf_buffer.seek(0)
+        yield from pdf_buffer
+
     return StreamingResponse(
-        content=pdf_buffer,
+        content=iterfile(),
         media_type="application/pdf",
         headers={
             "Content-Disposition": f"attachment; filename={filename}",