fix: scope analytics/flows/{tree_id} to requesting account

Any authenticated user could read flow analytics (session counts,
completion rates, CSAT) for any tree UUID. Now returns 404 if the
tree doesn't belong to the requesting account.

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

backend/app/api/endpoints/analytics.py

@@ -7,6 +7,7 @@ from sqlalchemy.ext.asyncio import AsyncSession
 
 from app.core.database import get_db
 from app.api.deps import get_current_active_user
+from app.core.filters import tenant_filter
 from app.models import User, Session, Tree, SessionRating
 from app.schemas.analytics import (
     TeamAnalyticsResponse, PersonalAnalyticsResponse, FlowAnalyticsResponse,
@@ -290,8 +291,13 @@ async def get_flow_analytics(
     current_user: User = Depends(get_current_active_user),
 ):
     """Analytics for a specific flow."""
-    # Verify tree exists
-    result = await db.execute(select(Tree).where(Tree.id == tree_id))
+    # Verify tree exists and belongs to the requesting user's account.
+    result = await db.execute(
+        select(Tree).where(
+            Tree.id == tree_id,
+            tenant_filter(Tree, current_user.account_id),
+        )
+    )
     tree = result.scalar_one_or_none()
     if not tree:
         raise HTTPException(status_code=404, detail="Flow not found")