added Validation rules

backend/src/middleware/Validation/Assignment.md

@@ -0,0 +1,20 @@
+## Shift Assignment
+
+### \[ACTION: update scheduled shift\]
+* Requires valid scheduled shift ID
+* Only updates assignedEmployees array
+* Requires authentication with valid token
+* Handles both JSON and non-JSON responses
+
+### \[ACTION: assign shifts automatically\]
+* Requires shift plan, employees, and availabilities
+* Availability preferenceLevel must be 1, 2, or 3
+* Constraints must be an array (converts non-array to empty array)
+* All employees must have valid availability data
+
+### \[ACTION: get scheduled shifts\]
+* Requires valid plan ID
+* Automatically fixes data structure inconsistencies:
+  - timeSlotId mapping (handles both naming conventions)
+  - requiredEmployees fallback to 2 if missing
+  - assignedEmployees fallback to empty array if missing