Refine PLC algorithm documentation for lighting control and EtherCAT integration

- Updated the output structure for `struct_room_outs` to focus solely on light states, removing unnecessary status feedback fields.
- Simplified the control logic for lights 1 to 6, aligning with the new design approach for Option C.
- Added detailed instructions for declaring `EtherCAT_RelayFeedback` and `EtherCAT_Outputs` in the Global Variable List, enhancing clarity for integration with the EL2809 module.

This update improves the documentation's accuracy and usability for developers working on the home automation system.

codesys/src/GVL/GVL_IO.gvl

@@ -0,0 +1,27 @@
+(*
+  GVL: GVL_IO
+  Option C relay feedback only. EL2809 DO: map channels directly in the device tree
+  to NVL_Out (e.g. NVL_Out.l_masterBedroom.l_1..l_6, ...) and boiler relay.
+  Initialize EtherCAT_RelayFeedback to zero at startup (or use default init).
+*)
+VAR_GLOBAL
+    // ---------- Option C: relay feedback (copy of output for next cycle) ----------
+    EtherCAT_RelayFeedback: STRUCT
+        masterBedroom: struct_room_outs;
+        masterBathroom: struct_room_outs;
+        bedroom_1: struct_room_outs;
+        bedroom_2: struct_room_outs;
+        bathroom: struct_room_outs;
+        guest_wc: struct_room_outs;
+        kitchen: struct_room_outs;
+        pantry: struct_room_outs;
+        livingRoom: struct_room_outs;
+        diningRoom: struct_room_outs;
+        entrance: struct_room_outs;
+        hallway: struct_room_outs;
+        veranda: struct_room_outs;
+        front: struct_room_outs;
+        back: struct_room_outs;
+        side: struct_room_outs;
+    END_STRUCT;
+END_VAR

codesys/src/GVL/GVL_NVL_placeholders.gvl

@@ -0,0 +1,48 @@
+(*
+  GVL: NVL stubs (or replace by CODESYS Network Variable lists NVL_In / NVL_Out).
+  In the real project, bind these to your UDP/network variable sender/receiver.
+  DI_Emergency_Stop: link to physical input or leave FALSE.
+*)
+VAR_GLOBAL
+    NVL_In: STRUCT
+        masterBedroom: struct_room_cmds;
+        masterBathroom: struct_room_cmds;
+        bedroom_1: struct_room_cmds;
+        bedroom_2: struct_room_cmds;
+        bathroom: struct_room_cmds;
+        guestWc: struct_room_cmds;
+        kitchen: struct_room_cmds;
+        pantry: struct_room_cmds;
+        livingRoom: struct_room_cmds;
+        dinningRoom: struct_room_cmds;
+        entrance: struct_room_cmds;
+        hallway: struct_room_cmds;
+        outVeranda: struct_room_cmds;
+        outFront: struct_room_cmds;
+        outBack: struct_room_cmds;
+        outSide: struct_room_cmds;
+        boiler: struct_boiler_cmd;
+    END_STRUCT;
+
+    NVL_Out: STRUCT
+        l_masterBedroom: struct_room_outs;
+        l_masterBathroom: struct_room_outs;
+        l_bedroom_1: struct_room_outs;
+        l_bedroom_2: struct_room_outs;
+        l_bathroom: struct_room_outs;
+        l_guestWc: struct_room_outs;
+        l_kitchen: struct_room_outs;
+        l_pantry: struct_room_outs;
+        l_livingRoom: struct_room_outs;
+        l_dinningRoom: struct_room_outs;
+        l_entrance: struct_room_outs;
+        l_hallway: struct_room_outs;
+        l_outVeranda: struct_room_outs;
+        l_outFront: struct_room_outs;
+        l_outBack: struct_room_outs;
+        l_outSide: struct_room_outs;
+        boiler_status: struct_boiler_status;
+    END_STRUCT;
+
+    DI_Emergency_Stop: BOOL := FALSE;
+END_VAR