feat: USDA FoodData Central per-ingredient nutrition lookup (v0.70.0)

estimateNutrition() (lib/ai/features/estimate-nutrition.ts) is now a
hybrid: for each ingredient, estimateGrams() (lib/ingredient-grams.ts)
converts its quantity+unit to grams where possible (weight units
exactly; volume units -- cup/tbsp/tsp/ml/l/etc -- via a 1ml~=1g water-
density approximation, documented as a real simplification but far
better than skipping them). Convertible ingredients get looked up in
USDA FoodData Central (lib/usda.ts, SR Legacy + Survey (FNDDS)
datasets -- the two suited to generic/raw ingredients, not Branded
packaged products or narrower Foundation) and summed. Whatever's left
(count-based units like "2 cloves", no USDA match, or USDA_API_KEY
unset entirely) goes through one AI call asking for just that
subset's total contribution, which sums directly with the USDA
totals -- no whole-recipe AI estimate to reconcile against.

Same exported signature and return shape as before
(NutritionEstimate / {perServing: {...}}), so every existing caller
(the nutrition route, meal-plan generation) gets more accurate
results automatically once USDA_API_KEY is set in Admin -> Settings,
with zero behavior change when it isn't.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

apps/web/lib/changelog.ts

@@ -1,5 +1,5 @@
 // Mirrors CHANGELOG.md at the repo root — update both together.
-export const APP_VERSION = "0.69.0";
+export const APP_VERSION = "0.70.0";
 
 export type ChangelogEntry = {
   version: string;
@@ -11,6 +11,13 @@ export type ChangelogEntry = {
 };
 
 export const CHANGELOG: ChangelogEntry[] = [
+  {
+    version: "0.70.0",
+    date: "2026-07-22 09:30",
+    added: [
+      "Recipe nutrition estimation now looks up real per-ingredient data from USDA FoodData Central (for ingredients whose quantity/unit converts to grams — e.g. \"200g flour\", \"2 tbsp oil\") and only asks AI to estimate whatever's left (count-based units like \"2 cloves\", or ingredients with no USDA match). Configure USDA_API_KEY in Admin → Settings (free, no partnership needed) — unset, it falls back to the previous fully-AI-estimated behavior exactly as before.",
+    ],
+  },
   {
     version: "0.69.0",
     date: "2026-07-22 09:00",