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/app-store-listing.md

@@ -21,7 +21,7 @@ You're not imagining it. It's called shrinkflation — and it's costing the aver
 CartSnitch helps you catch it.
 
 **What CartSnitch does:**
-- Tracks unit prices on thousands of grocery products
+- Tracks unit prices on grocery products
 - Alerts you when a product you buy regularly gets smaller or more expensive
 - Compares your total grocery bill across stores so you always know where to shop cheapest
 
@@ -31,7 +31,7 @@ Brands know you'll notice a price increase before you'll notice a smaller packag
 CartSnitch tracks the unit price — price per ounce, price per use — so you see exactly what's happening.
 
 **Key features:**
-- Unit price tracking across thousands of products
+- Unit price tracking across grocery products
 - Personalized price alerts on products you buy regularly
 - Store comparison — see your total basket cost at different stores
 - Shrinkflation tracker — see which products have changed the most
@@ -55,7 +55,7 @@ You're not imagining it. It's called shrinkflation — and it's costing the aver
 CartSnitch helps you catch it.
 
 **What CartSnitch does:**
-- Tracks unit prices on thousands of grocery products
+- Tracks unit prices on grocery products
 - Alerts you when a product you buy regularly gets smaller or more expensive
 - Compares your total grocery bill across stores so you always know where to shop cheapest
 
@@ -65,7 +65,7 @@ Brands know you'll notice a price increase before you'll notice a smaller packag
 CartSnitch tracks the unit price — price per ounce, price per use — so you see exactly what's happening.
 
 **Key features:**
-- Unit price tracking across thousands of products
+- Unit price tracking across grocery products
 - Personalized price alerts on products you buy regularly
 - Store comparison — see your total basket cost at different stores
 - Shrinkflation tracker — see which products have changed the most
@@ -82,7 +82,7 @@ CartSnitch tracks the unit price — price per ounce, price per use — so you s
 
 ## Feature Highlights (4 bullets, Google Play)
 
-- Track unit prices on thousands of products
+- Track unit prices on grocery products
 - Personalized alerts when products you buy change
 - Compare grocery costs across stores
 - See the biggest shrinkflation offenders