feat: merge cartsnitch/api into api/ subdirectory

Consolidate API gateway service into monorepo.
Squashed from https://github.com/cartsnitch/api main (89bacb1).

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

src/cartsnitch_api/constants.py

@@ -0,0 +1,85 @@
+"""Constants and enums shared across CartSnitch services."""
+
+from enum import StrEnum
+
+
+class StoreSlug(StrEnum):
+    """Supported retailer slugs."""
+
+    MEIJER = "meijer"
+    KROGER = "kroger"
+    TARGET = "target"
+
+
+class AccountStatus(StrEnum):
+    """User store account link status."""
+
+    ACTIVE = "active"
+    EXPIRED = "expired"
+    ERROR = "error"
+
+
+class DiscountType(StrEnum):
+    """Coupon discount type."""
+
+    PERCENT = "percent"
+    FIXED = "fixed"
+    BOGO = "bogo"
+    BUY_X_GET_Y = "buy_x_get_y"
+
+
+class PriceSource(StrEnum):
+    """Source of a price observation."""
+
+    RECEIPT = "receipt"
+    CATALOG = "catalog"
+    WEEKLY_AD = "weekly_ad"
+
+
+class EventType(StrEnum):
+    """Redis pub/sub event types."""
+
+    RECEIPTS_INGESTED = "cartsnitch.receipts.ingested"
+    PRICES_UPDATED = "cartsnitch.prices.updated"
+    PRODUCTS_NORMALIZED = "cartsnitch.products.normalized"
+    COUPONS_UPDATED = "cartsnitch.coupons.updated"
+    ALERT_PRICE_INCREASE = "cartsnitch.alerts.price_increase"
+    ALERT_SHRINKFLATION = "cartsnitch.alerts.shrinkflation"
+
+
+class ProductCategory(StrEnum):
+    """Top-level product categories."""
+
+    PRODUCE = "produce"
+    DAIRY = "dairy"
+    MEAT = "meat"
+    BAKERY = "bakery"
+    FROZEN = "frozen"
+    PANTRY = "pantry"
+    BEVERAGES = "beverages"
+    SNACKS = "snacks"
+    HOUSEHOLD = "household"
+    PERSONAL_CARE = "personal_care"
+    OTHER = "other"
+
+
+class MatchConfidence(StrEnum):
+    """Confidence level for product matching."""
+
+    HIGH = "high"
+    MEDIUM = "medium"
+    LOW = "low"
+
+
+class SizeUnit(StrEnum):
+    """Standardized product size units."""
+
+    OZ = "oz"
+    FL_OZ = "fl_oz"
+    LB = "lb"
+    G = "g"
+    KG = "kg"
+    ML = "ml"
+    L = "l"
+    CT = "ct"
+    PK = "pk"