Fix math, citation, and receipt scanning status in vs-flipp article

- Correct unit price increase from 13.8% to 16.1%: (18/15.5 - 1 = 16.1%)
  13.8% was the size reduction, not the unit price increase
- Remove fabricated USDA FoodData Central citation; USDA FDC is a
  nutrient database and does not produce shrinkflation cost estimates
- Remove unsupported $80-120/year claim (no verifiable source)
- Change "Receipt scanning: In development" to "Planned" — receipt
  ingestion is P3/someday-maybe, not actively in development
- Add YAML frontmatter to match blog article conventions
- Remove USDA FoodData Central from methodology citations

Addresses CTO and CEO review feedback on PR #36.

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

content/marketing/blog/cartsnitch-vs-flipp.md

@@ -0,0 +1,53 @@
+---
+title: "CartSnitch vs Flipp: Which App Actually Helps You Save More on Groceries?"
+slug: cartsnitch-vs-flipp
+status: draft
+version: 1.1
+last_updated: 2026-03-22
+description: "Flipp shows you this week's sale prices. CartSnitch tracks unit prices over time and catches shrinkflation before you notice. Here's when each tool wins."
+tags: ["comparison", "flipp", "unit-price", "shrinkflation", "smart-shopping"]
+target_publish: "2026-05"
+---
+
+# CartSnitch vs Flipp: Which App Actually Helps You Save More on Groceries?
+
+Both CartSnitch and Flipp help you find deals on groceries, but they work differently. Here is how they compare on the features that matter most for saving money.
+
+## What Is Flipp?
+
+Flipp is a digital flyer app that lets you browse weekly grocery ads from multiple retailers in one place. You can clip coupons and create a shopping list from featured deals.
+
+## What Is CartSnitch?
+
+CartSnitch is a grocery price tracking and shrinkflation detection app. It monitors unit prices over time, alerts you when products you buy regularly change in size or price, and compares prices across stores.
+
+## Key Differences
+
+| Feature | CartSnitch | Flipp |
+|---------|-----------|-------|
+| **Price tracking over time** | ✅ Tracks unit prices continuously | ❌ Shows only current weekly ad prices |
+| **Shrinkflation detection** | ✅ Alerts when product sizes shrink | ❌ No shrinkflation monitoring |
+| **Unit price normalization** | ✅ Compares price-per-oz or price-per-unit across brands and stores | ❌ Compares only advertised sale prices |
+| **Store comparison** | ✅ Compares total basket cost across stores | ❌ Single-store flyer browsing |
+| **Price alerts** | ✅ Alerts on products you track | ❌ No personalized tracking |
+| **Receipt scanning** | Planned | ❌ No |
+
+## The Core Difference: Unit Price vs Sale Price
+
+Flipp shows you where items are on sale this week. CartSnitch shows you when brands are quietly shrinking products or when stores are charging more than competitors — even if neither is "on sale."
+
+**Example:** A cereal brand reduces its box from 18 oz to 15.5 oz. The shelf price stays the same. Flipp shows no deal. CartSnitch flags it as a 16.1% unit price increase.
+
+This is shrinkflation. A shopper buying the same cereal box at the same shelf price is now paying 16.1% more per ounce — without any price tag ever changing.
+
+## Which App Saves You More?
+
+**If you shop sales and clip coupons:** Flipp has a large catalog of weekly ad matchups.
+
+**If you want to track the actual cost of your grocery basket over time and catch every hidden price increase:** CartSnitch is built for this.
+
+Many users end up using both — Flipp for browsing weekly deals, CartSnitch for monitoring the real cost of their regular purchases.
+
+## Methodology
+
+CartSnitch tracks unit prices (price ÷ size) across product categories using manufacturer and retailer data. Shrinkflation percentage calculated as: `(new_price/new_size) / (old_price/old_size) - 1`. Comparisons are based on publicly available manufacturer packaging data.