Implement Excel webhook integration

Features:
- Migration 0007: shipping_date column with automatic next-business-day calculation
- New function trigger_excel_webhook() in order-import.php
- SQL query for extracting Excel data from ERP database
- Integration after successful order import
- Documentation for n8n Postgres node configuration

Changes:
1. db/migrations/0007_phase1_excel_webhook.sql - adds shipping_date column, trigger, next-business-day function
2. order-import.php - adds trigger_excel_webhook() function and integration point
3. docs/EXAKTE_POSTGRES_QUERY.sql - exact SQL query for n8n Postgres node
4. docs/N8N_POSTGRES_QUERY.md - comprehensive documentation
5. docs/N8N_POSTGRES_NODE.* - n8n node configurations
6. docs/N8N_EXCEL_WORKFLOW.json - complete workflow JSON
7. docs/N8N_NODE_COPY_PASTE.md - copy-paste ready instructions

The implementation triggers an Excel webhook after every successful order import, sending all necessary data for Excel bookkeeping to n8n.

db/migrations/0007_phase1_excel_webhook.sql

@@ -0,0 +1,44 @@
+BEGIN;
+
+-- 1. Add shipping_date column to sales_order
+ALTER TABLE sales_order ADD COLUMN shipping_date TIMESTAMP NULL;
+
+-- 2. Function to calculate next business day (exclude weekends)
+CREATE OR REPLACE FUNCTION fn_next_business_day(order_date TIMESTAMP)
+RETURNS TIMESTAMP AS $$
+DECLARE
+    next_day TIMESTAMP;
+    dow INT;
+BEGIN
+    next_day := order_date + INTERVAL '1 day';
+    dow := EXTRACT(DOW FROM next_day); -- 0=Sunday, 1=Monday, ..., 6=Saturday
+    
+    -- Skip weekends
+    IF dow = 0 THEN -- Sunday
+        next_day := next_day + INTERVAL '1 day';
+    ELSIF dow = 6 THEN -- Saturday
+        next_day := next_day + INTERVAL '2 days';
+    END IF;
+    
+    RETURN next_day;
+END;
+$$ LANGUAGE plpgsql;
+
+-- 3. Trigger for automatic shipping_date calculation
+CREATE OR REPLACE FUNCTION fn_auto_shipping_date()
+RETURNS TRIGGER AS $$
+BEGIN
+    -- Only calculate for new orders or when shipping_date is empty
+    IF NEW.shipping_date IS NULL AND NEW.order_date IS NOT NULL THEN
+        NEW.shipping_date := fn_next_business_day(NEW.order_date);
+    END IF;
+    RETURN NEW;
+END;
+$$ LANGUAGE plpgsql;
+
+CREATE TRIGGER trg_auto_shipping_date
+    BEFORE INSERT OR UPDATE ON sales_order
+    FOR EACH ROW
+    EXECUTE FUNCTION fn_auto_shipping_date();
+
+COMMIT;