Step 1: Add PricingConfig model and PricingRepository

- Create PricingConfig model with all required fields (premium settings, trade limits)
- Implement PricingRepository with singleton pattern (get_current, create_or_update)
- Add comprehensive tests for repository functionality
- Export model and repository in __init__.py files

backend/repositories/pricing.py

@@ -0,0 +1,83 @@
+"""Pricing repository for database queries."""
+
+from sqlalchemy import select
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from models import PricingConfig
+
+
+class PricingRepository:
+    """Repository for pricing configuration database queries."""
+
+    def __init__(self, db: AsyncSession):
+        self.db = db
+
+    async def get_current(self) -> PricingConfig | None:
+        """Get the current pricing configuration (singleton).
+
+        Returns:
+            PricingConfig if exists, None otherwise
+        """
+        result = await self.db.execute(select(PricingConfig).limit(1))
+        return result.scalar_one_or_none()
+
+    async def create_or_update(
+        self,
+        premium_buy: int,
+        premium_sell: int,
+        small_trade_threshold_eur: int,
+        small_trade_extra_premium: int,
+        eur_min_buy: int,
+        eur_max_buy: int,
+        eur_min_sell: int,
+        eur_max_sell: int,
+    ) -> PricingConfig:
+        """Create or update pricing configuration (singleton pattern).
+
+        If no config exists, creates a new one.
+        If config exists, updates the existing record.
+
+        Args:
+            premium_buy: Premium percentage for BUY direction (-100 to 100)
+            premium_sell: Premium percentage for SELL direction (-100 to 100)
+            small_trade_threshold_eur: Threshold in EUR cents for small trade
+                extra premium
+            small_trade_extra_premium: Extra premium percentage for small trades
+                (-100 to 100)
+            eur_min_buy: Minimum trade amount in EUR cents for BUY
+            eur_max_buy: Maximum trade amount in EUR cents for BUY
+            eur_min_sell: Minimum trade amount in EUR cents for SELL
+            eur_max_sell: Maximum trade amount in EUR cents for SELL
+
+        Returns:
+            Created or updated PricingConfig record
+        """
+        config = await self.get_current()
+
+        if config is None:
+            # Create new config
+            config = PricingConfig(
+                premium_buy=premium_buy,
+                premium_sell=premium_sell,
+                small_trade_threshold_eur=small_trade_threshold_eur,
+                small_trade_extra_premium=small_trade_extra_premium,
+                eur_min_buy=eur_min_buy,
+                eur_max_buy=eur_max_buy,
+                eur_min_sell=eur_min_sell,
+                eur_max_sell=eur_max_sell,
+            )
+            self.db.add(config)
+        else:
+            # Update existing config
+            config.premium_buy = premium_buy
+            config.premium_sell = premium_sell
+            config.small_trade_threshold_eur = small_trade_threshold_eur
+            config.small_trade_extra_premium = small_trade_extra_premium
+            config.eur_min_buy = eur_min_buy
+            config.eur_max_buy = eur_max_buy
+            config.eur_min_sell = eur_min_sell
+            config.eur_max_sell = eur_max_sell
+
+        await self.db.commit()
+        await self.db.refresh(config)
+        return config