TICKET-004: Day summary endpoint

- GET /api/log/summary?date= with totals vs historical target
- Nutrition math consolidated in services/nutrition.py (weight vs count)
- Null nutrition contributes 0; meals contribute 0 (TODO TICKET-007)
- Full suite green (104 passed)

backend/routers/log.py

@@ -6,7 +6,7 @@ from fastapi import APIRouter, Depends, HTTPException
 from sqlalchemy.orm import Session
 
 from database import get_db
-from schemas import LogEntryCreate, LogEntryRead, LogEntryUpdate
+from schemas import DaySummaryResponse, LogEntryCreate, LogEntryRead, LogEntryUpdate
 from services import log as svc
 
 router = APIRouter(prefix="/api/log", tags=["log"])
@@ -29,6 +29,12 @@ def create_log_entry(data: LogEntryCreate, db: Session = Depends(get_db)):
         raise HTTPException(status_code=404, detail=str(e))
 
 
+@router.get("/summary", response_model=DaySummaryResponse)
+def get_day_summary(date: date, db: Session = Depends(get_db)):
+    """Computed nutrition totals for the day vs. the applicable target (§3.3)."""
+    return svc.get_day_summary(db, date)
+
+
 @router.put("/{entry_id}", response_model=LogEntryRead)
 def update_log_entry(entry_id: int, data: LogEntryUpdate, db: Session = Depends(get_db)):
     """Update quantity, meal_slot, and/or sort_order.