Fix content issues flagged by CEO and QA (PR #42 review)

Critical fixes:
- stores.md: Correct supported retailers to Meijer, Kroger, Target.
  Remove Safeway (never scoped). Replace named Coming Soon list with
  generic demand-based evaluation language.
- privacy.md: Replace all OAuth/API claims with accurate language
  describing read-only headless browser access to loyalty portals.
- about.md: Remove "price gouging on our roadmap" claim.
  Clarify USDA FoodData Central is reference data only, not a source
  of price data.
- blog/price-gouging-vs-shrinkflation.md: Remove roadmap claim.
  Remove implication that price gouging detection is coming.
- methodology.md: Fix cereal example math — 16.2% → 16.1%.
  Use raw values per the stated formula. Clarify USDA FoodData
  Central role for package sizing baselines only.
- how-it-works.md: Correct retailers. Remove "(yet)" from receipt
  claim. Clarify USDA FoodData Central is reference data.

Important fixes:
- press-kit.md: Correct supported stores. Remove USDA FoodData Central
  from dollar-cost attribution — reattribute to CartSnitch analysis of
  manufacturer packaging data.
- app-store-listing.md: Remove "thousands of products" claims
  (pre-launch beta, quantity unverified).
- social/launch-day-posts.md: Remove "thousands of products" claim.
  Correct retailer list.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

content/marketing/how-it-works.md

@@ -15,9 +15,9 @@ CartSnitch tracks unit prices automatically — so you don't have to do the math
 ## How We Track Prices
 
 CartSnitch pulls pricing data from:
-- **Store loyalty programs** — Kroger, Safeway (and more coming) — when you connect your account
+- **Store loyalty accounts** — Meijer, Kroger, and Target — when you connect your account
 - **Public manufacturer data** — packaging changes, suggested retail prices
-- **USDA FoodData Central** — reference data for nutrition and package sizing
+- **USDA FoodData Central** — reference data for package sizing baselines
 
 We calculate unit price for every product we track:
 
@@ -63,7 +63,7 @@ This is different from just comparing the price of one item. Some stores are che
 
 ## What We Don't Do
 
-- **We don't collect receipts** (yet) — Store account connections give us enough data to track prices and compare baskets
+- **We don't collect receipts** — Store account connections give us enough data to track prices and compare baskets
 - **We don't have every product** — Beta is limited to supported stores and categories. We're adding more every week.
 - **We don't affect shelf prices** — We show you the data. What you do with it is up to you.