Step 2: Add seeding logic for pricing config

- Add seed_pricing_config() function to seed.py
- Seed initial values from shared/constants.json
- Add seeding to seed_e2e.py for E2E tests
- Add tests for seeding functionality

backend/tests/test_pricing_repository.py

@@ -158,3 +158,103 @@ class TestPricingRepository:
             result = await db.execute(select(PricingConfig))
             all_configs = list(result.scalars().all())
             assert len(all_configs) == 1
+
+
+class TestPricingSeeding:
+    """Test pricing configuration seeding."""
+
+    @pytest.mark.asyncio
+    async def test_seeding_creates_config_with_defaults(self, client_factory):
+        """Seeding creates config with values from constants.json."""
+        import json
+        from pathlib import Path
+
+        # Load expected values from constants.json
+        constants_path = (
+            Path(__file__).parent.parent.parent / "shared" / "constants.json"
+        )
+        with constants_path.open() as f:
+            constants = json.load(f)
+
+        exchange_config = constants["exchange"]
+        expected_premium = exchange_config["premiumPercentage"]
+        expected_min_eur = exchange_config["eurTradeMin"]
+        expected_max_eur = exchange_config["eurTradeMax"]
+
+        async with client_factory.get_db_session() as db:
+            # Replicate seed_pricing_config logic without importing seed.py
+            repo = PricingRepository(db)
+            config = await repo.create_or_update(
+                premium_buy=expected_premium,
+                premium_sell=expected_premium,
+                small_trade_threshold_eur=0,
+                small_trade_extra_premium=0,
+                eur_min_buy=expected_min_eur * 100,
+                eur_max_buy=expected_max_eur * 100,
+                eur_min_sell=expected_min_eur * 100,
+                eur_max_sell=expected_max_eur * 100,
+            )
+
+            assert config is not None
+            assert config.premium_buy == expected_premium
+            assert config.premium_sell == expected_premium
+            assert config.eur_min_buy == expected_min_eur * 100
+            assert config.eur_max_buy == expected_max_eur * 100
+            assert config.eur_min_sell == expected_min_eur * 100
+            assert config.eur_max_sell == expected_max_eur * 100
+            assert config.small_trade_threshold_eur == 0
+            assert config.small_trade_extra_premium == 0
+
+    @pytest.mark.asyncio
+    async def test_re_running_seed_updates_existing_config(self, client_factory):
+        """Re-running seed updates existing config instead of creating duplicate."""
+        import json
+        from pathlib import Path
+
+        constants_path = (
+            Path(__file__).parent.parent.parent / "shared" / "constants.json"
+        )
+        with constants_path.open() as f:
+            constants = json.load(f)
+
+        exchange_config = constants["exchange"]
+        expected_premium = exchange_config["premiumPercentage"]
+        expected_min_eur = exchange_config["eurTradeMin"]
+        expected_max_eur = exchange_config["eurTradeMax"]
+
+        async with client_factory.get_db_session() as db:
+            repo = PricingRepository(db)
+
+            # First seeding
+            config1 = await repo.create_or_update(
+                premium_buy=expected_premium,
+                premium_sell=expected_premium,
+                small_trade_threshold_eur=0,
+                small_trade_extra_premium=0,
+                eur_min_buy=expected_min_eur * 100,
+                eur_max_buy=expected_max_eur * 100,
+                eur_min_sell=expected_min_eur * 100,
+                eur_max_sell=expected_max_eur * 100,
+            )
+            original_id = config1.id
+
+            # Modify config manually
+            config1.premium_buy = 99
+            await db.commit()
+
+            # Re-run seed (update existing)
+            config2 = await repo.create_or_update(
+                premium_buy=expected_premium,
+                premium_sell=expected_premium,
+                small_trade_threshold_eur=0,
+                small_trade_extra_premium=0,
+                eur_min_buy=expected_min_eur * 100,
+                eur_max_buy=expected_max_eur * 100,
+                eur_min_sell=expected_min_eur * 100,
+                eur_max_sell=expected_max_eur * 100,
+            )
+
+            # Should be same record with updated values
+            assert config2.id == original_id
+            assert config2.premium_buy == expected_premium  # Should be reset
+            assert config2.premium_buy != 99