Initial project scaffold: FastAPI backend + Svelte 5 frontend

Backend (uv): FastAPI app with routers (foods, log, targets, OFF proxy),
SQLAlchemy models, Pydantic schemas, migration runner + 0001 initial schema,
example pytest suite (7 tests).
Frontend (npm): Vite 7 + Svelte 5 runes, lib/ (api, stores, scanner, format)
per spec §7, placeholder components, example vitest suite (4 tests).
SPEC.md §1: registered uvicorn and Vitest (rule §8.3.3).

backend/services/nutrition.py

@@ -0,0 +1,30 @@
+"""Nutrition math — the ONLY place nutrition is computed (spec §8.1 rule 1).
+
+Routers never compute nutrition; the frontend never re-derives it.
+`quantity` is interpreted by context (spec §2.1):
+  - unit_type "weight": quantity is grams; nutrition = (quantity / 100) × per_unit
+  - unit_type "count":  quantity is item count; nutrition = quantity × per_unit
+  - meal:               quantity is a scaling factor (1.0 = one full meal)
+"""
+
+from models import Food
+
+
+def scale_to_quantity(per_unit: float | None, quantity: float, unit_type: str) -> float:
+    """Scale a per-unit nutrition value to a logged quantity. Missing values count as 0."""
+    if per_unit is None:
+        return 0.0
+    if unit_type == "weight":
+        return per_unit * quantity / 100.0
+    if unit_type == "count":
+        return per_unit * quantity
+    raise ValueError(f"unknown unit_type: {unit_type!r}")
+
+
+def entry_calories(food: Food, quantity: float) -> float:
+    """Calories for a single (non-meal) food at a logged quantity.
+
+    TODO: handle is_meal foods by summing scaled component nutrition
+    (recursively, with cycle detection — spec §2.2).
+    """
+    return scale_to_quantity(food.calories_per_unit, quantity, food.unit_type)