Add data migration script for Serial No grades

Run after bench migrate. Maps cosmetic_grade C# values to new grade field:
- C5-C9 → High
- C4 → Med
- C3 → Low
- C0-C2, blank → Flagged

Requires: bench migrate has already created the new fields.

westech_r2/migrations/migrate_serial_grades.py

@@ -0,0 +1,79 @@
+"""
+Data Migration: Populate new Serial No fields from existing data.
+
+Run this IMMEDIATELY after `bench migrate` on production.
+Requires: all new fields already exist (grade, cpu_test, ram_test, etc.)
+
+Maps cosmetic_grade C# values → new grade field:
+  C5-C9 → High
+  C4 → Med
+  C3 → Low
+  C0-C2, blank, anything else → Flagged
+"""
+
+import frappe
+from frappe.utils import now
+
+def run():
+    print(f"[{now()}] Starting Serial No grade migration...")
+    
+    serials = frappe.get_all("Serial No",
+        fields=["name", "cosmetic_grade", "grade", "pricing_status"],
+        limit_page_length=0
+    )
+    
+    stats = {"high": 0, "med": 0, "low": 0, "flagged": 0, "skipped": 0, "errors": 0}
+    
+    for i, s in enumerate(serials):
+        try:
+            cosmetic = (s.cosmetic_grade or "").strip().upper()
+            
+            # Map cosmetic_grade → new grade
+            if cosmetic in ("C5", "C6", "C7", "C8", "C9"):
+                new_grade = "High"
+            elif cosmetic == "C4":
+                new_grade = "Med"
+            elif cosmetic == "C3":
+                new_grade = "Low"
+            else:
+                new_grade = "Flagged"
+            
+            # Only update if grade is blank or old value
+            if s.grade and s.grade in ("High", "Med", "Low", "Flagged"):
+                stats["skipped"] += 1
+                continue
+            
+            # Determine pricing_status
+            if new_grade == "Flagged":
+                pricing_status = "Flagged"
+            else:
+                pricing_status = "Needs Pricing"
+            
+            frappe.db.set_value("Serial No", s.name, {
+                "grade": new_grade,
+                "pricing_status": pricing_status
+            })
+            
+            stats[new_grade.lower()] += 1
+            
+            if (i + 1) % 1000 == 0:
+                frappe.db.commit()
+                print(f"  Processed {i + 1}/{len(serials)}...")
+        
+        except Exception as e:
+            stats["errors"] += 1
+            frappe.log_error(f"Migration error for {s.name}: {e}", "Serial Grade Migration")
+    
+    frappe.db.commit()
+    
+    print(f"\n[{now()}] Migration complete!")
+    print(f"  Total Serial Nos: {len(serials)}")
+    print(f"  High: {stats['high']}")
+    print(f"  Med: {stats['med']}")
+    print(f"  Low: {stats['low']}")
+    print(f"  Flagged: {stats['flagged']}")
+    print(f"  Skipped (already new grade): {stats['skipped']}")
+    print(f"  Errors: {stats['errors']}")
+
+if __name__ == "__main__":
+    run()