feat: add script to create inventory entries for products

Created script to populate inventory table for products that have 0 inventory.

Issue:
- Products had 0 available_inventory because inventory table was empty
- available_inventory is calculated from inventory_entries relationship
- Empty inventory table = 0 inventory for all products
- Add to cart fails when inventory is 0

Solution:
- Create inventory entries for all products
- Each product gets 100 units in 'Main Warehouse'
- Script can be run multiple times (only creates missing entries)

Usage:
  python scripts/create_inventory.py

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

scripts/create_inventory.py

@@ -0,0 +1,87 @@
+#!/usr/bin/env python3
+"""
+Create Inventory Entries for Products
+
+This script creates inventory entries for all products that don't have inventory.
+Each product gets 100 units in stock.
+"""
+
+import sys
+from pathlib import Path
+
+# Add project root to path
+sys.path.insert(0, str(Path(__file__).parent.parent))
+
+import sqlite3
+from datetime import datetime, UTC
+import os
+from dotenv import load_dotenv
+
+# Load environment variables
+load_dotenv()
+
+# Get database URL
+database_url = os.getenv('DATABASE_URL', 'wizamart.db')
+db_path = database_url.replace('sqlite:///', '')
+
+print(f"📦 Creating inventory entries in {db_path}...")
+
+conn = sqlite3.connect(db_path)
+cursor = conn.cursor()
+
+# Get products without inventory
+cursor.execute("""
+    SELECT p.id, p.vendor_id, p.product_id 
+    FROM products p
+    LEFT JOIN inventory i ON p.id = i.product_id
+    WHERE i.id IS NULL
+""")
+products_without_inventory = cursor.fetchall()
+
+if not products_without_inventory:
+    print("✅ All products already have inventory entries")
+    conn.close()
+    sys.exit(0)
+
+print(f"📦 Creating inventory for {len(products_without_inventory)} products...")
+
+# Create inventory entries
+for product_id, vendor_id, sku in products_without_inventory:
+    cursor.execute("""
+        INSERT INTO inventory (
+            vendor_id,
+            product_id,
+            location,
+            quantity,
+            reserved_quantity,
+            created_at,
+            updated_at
+        ) VALUES (?, ?, ?, ?, ?, ?, ?)
+    """, (
+        vendor_id,
+        product_id,
+        'Main Warehouse',
+        100,  # Total quantity
+        0,    # Reserved quantity
+        datetime.now(UTC),
+        datetime.now(UTC)
+    ))
+
+conn.commit()
+
+print(f"✅ Created inventory entries for {len(products_without_inventory)} products")
+
+# Show stats
+cursor.execute("SELECT COUNT(*) FROM inventory")
+total_count = cursor.fetchone()[0]
+print(f"\n📊 Total inventory entries: {total_count}")
+
+cursor.execute("SELECT product_id, location, quantity, reserved_quantity FROM inventory LIMIT 5")
+print("\n📦 Sample inventory:")
+for row in cursor.fetchall():
+    available = row[2] - row[3]
+    print(f"  Product ID {row[0]}: {available} available at {row[1]}")
+
+conn.close()
+
+print("\n✅ Done!")