Add OTC sales UI with direct sales support

- Create OTC UI form at public/otc/index.php
- Add API endpoint public/api/otc-order.php
- Extract shared DB connection to includes/db.php
- Add migration for OTC products (0006_phase1_otc_products.sql)
- Support order_source='direct' with automatic DIR- reference generation
- Include billing address capture with default values
- Add payment methods cash and paypal for direct sales
- Implement stock allocation and inventory management

db/migrations/0006_phase1_otc_products.sql

@@ -0,0 +1,107 @@
+BEGIN;
+
+-- OTC products for direct sales
+INSERT INTO product (sku, name, status, uom) VALUES
+  ('SHIITAKE-50ML', 'PURE Shiitake Extrakt Tinktur 50ml', 'active', 'unit'),
+  ('REISHI-50ML', 'PURE Reishi Extrakt Tinktur 50ml', 'active', 'unit'),
+  ('LIONSMANE-50ML', 'PURE Lion''s Mane Extrakt Tinktur 50ml', 'active', 'unit'),
+  ('CHAGA-50ML', 'PURE Chaga Aroma Extrakt Tinktur 50ml', 'active', 'unit')
+ON CONFLICT (sku) DO UPDATE SET
+  name = EXCLUDED.name,
+  status = EXCLUDED.status,
+  uom = EXCLUDED.uom,
+  updated_at = NOW();
+
+-- Create sellable items for OTC products
+INSERT INTO sellable_item (item_code, display_name, status)
+SELECT 
+  'OTC-' || p.id,
+  p.name,
+  'active'
+FROM product p
+WHERE p.sku IN ('SHIITAKE-50ML', 'REISHI-50ML', 'LIONSMANE-50ML', 'CHAGA-50ML')
+ON CONFLICT (item_code) DO UPDATE SET
+  display_name = EXCLUDED.display_name,
+  status = EXCLUDED.status,
+  updated_at = NOW();
+
+-- Link sellable items to products
+INSERT INTO sellable_item_component (sellable_item_id, product_id, qty_per_item)
+SELECT 
+  si.id,
+  p.id,
+  1.0
+FROM sellable_item si
+JOIN product p ON p.name = si.display_name
+WHERE p.sku IN ('SHIITAKE-50ML', 'REISHI-50ML', 'LIONSMANE-50ML', 'CHAGA-50ML')
+ON CONFLICT (sellable_item_id, product_id) DO UPDATE SET
+  qty_per_item = EXCLUDED.qty_per_item,
+  updated_at = NOW();
+
+-- Ensure we have current lots for OTC products
+DO $$
+DECLARE
+  prod_record RECORD;
+  current_lot_id BIGINT;
+  open_lot_id BIGINT;
+BEGIN
+  FOR prod_record IN 
+    SELECT id FROM product 
+    WHERE sku IN ('SHIITAKE-50ML', 'REISHI-50ML', 'LIONSMANE-50ML', 'CHAGA-50ML')
+  LOOP
+    -- Check if current lot exists
+    SELECT id INTO current_lot_id
+    FROM stock_lot 
+    WHERE product_id = prod_record.id 
+      AND status = 'current'
+    LIMIT 1;
+    
+    IF current_lot_id IS NULL THEN
+      -- Check for open lot to promote
+      SELECT id INTO open_lot_id
+      FROM stock_lot 
+      WHERE product_id = prod_record.id 
+        AND status = 'open'
+      ORDER BY id
+      LIMIT 1;
+      
+      IF open_lot_id IS NULL THEN
+        -- Create both current and open lots
+        INSERT INTO stock_lot (product_id, lot_number, status)
+        VALUES (prod_record.id, 'OTC-INIT-' || prod_record.id, 'current')
+        RETURNING id INTO current_lot_id;
+        
+        INSERT INTO stock_lot (product_id, status)
+        VALUES (prod_record.id, 'open');
+        
+        -- Add initial stock
+        INSERT INTO stock_move (product_id, lot_id, from_location_id, to_location_id, qty, move_type, note)
+        SELECT 
+          prod_record.id,
+          current_lot_id,
+          NULL,
+          l.id,
+          100.0,
+          'in',
+          'Initial OTC stock'
+        FROM location l 
+        WHERE l.type = 'storage'
+        ORDER BY l.id
+        LIMIT 1;
+      ELSE
+        -- Promote open lot to current
+        UPDATE stock_lot 
+        SET status = 'current',
+            lot_number = COALESCE(lot_number, 'OTC-' || prod_record.id || '-' || open_lot_id),
+            updated_at = NOW()
+        WHERE id = open_lot_id;
+        
+        -- Create new open lot
+        INSERT INTO stock_lot (product_id, status)
+        VALUES (prod_record.id, 'open');
+      END IF;
+    END IF;
+  END LOOP;
+END $$;
+
+COMMIT;