feat: add include_summary and detail_level to SessionExport schema

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/app/schemas/session.py

@@ -89,6 +89,9 @@ class SessionExport(BaseModel):
     include_outcome_notes: bool = True
     include_next_steps: bool = True
     max_step_index: Optional[int] = Field(None, ge=1, description="1-based inclusive step cutoff")
+    # Phase B
+    include_summary: bool = False
+    detail_level: Literal["standard", "full"] = "standard"
 
 
 class SessionComplete(BaseModel):