fix: add quality_filter_level to ProfileUpdate model (Issue #31)

The frontend was sending quality_filter_level to the backend, but the
Pydantic ProfileUpdate model didn't include this field, so it was
silently ignored. Profile updates never actually saved the filter.

This is why the charts didn't react to filter changes - the backend
database was never updated.

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

backend/models.py

@@ -27,6 +27,7 @@ class ProfileUpdate(BaseModel):
     height: Optional[float] = None
     goal_weight: Optional[float] = None
     goal_bf_pct: Optional[float] = None
+    quality_filter_level: Optional[str] = None  # Issue #31: Global quality filter
 
 
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