generator: auto-expand declarative plug lists with per-channel mapper

Add build_plugs() to flow2json.py: a flow can declare a plugs: table
({id, name, channels?}) plus single_plugs/hold_plugs lists and the
generator emits all plumbing automatically — state-in node, /set out node,
dashboard widget, and (for multi-channel devices) a mapper function that
toggles each channel (state_1/state_2) instead of the ignored shared
{state:TOGGLE} payload.

Rewrite zigbee-monitor.yaml to the declarative form; Dual Outlet - Couch
is multi-channel (channels: [1,2]). Adding a plug is one line, no manual
node/wire duplication. Single press toggles 5 devices (couch via mapper
verified E2E ON/OFF), hold-release still DJ Booth only.

Refs: david/nr-flow-validator#2

flows/zigbee-monitor.yaml

@@ -5,17 +5,6 @@ brokers:
     host: mosquitto
     port: 1883
 
-# Plugs toggled on brief single press
-single_plugs:
-  - Squiggle
-  - Sideboard Lamp
-  - Bamboo Lights
-  - Dual Outlet - Couch
-
-# Plugs toggled on press-hold-release (action: "release" after a "hold")
-hold_plugs:
-  - DJ Booth
-
 dashboards:
   - base: Dashboard
     pages:
@@ -28,38 +17,35 @@ dashboards:
 
 flows:
   - tab: Zigbee Monitor
-    description: Button dispatches single vs hold-release to different plug sets
+    description: Button dispatches single vs hold-release to different plug sets.
+      Plug plumbing (state-in, /set out, dashboard widget, per-channel mapper)
+      is generated by flow2json.py from the plugs lists below.
+
+    # Declarative plug set. channels:[] marks a multi-channel device, which gets
+    # a mapper that toggles each channel and a widget showing each state_N.
+    plugs:
+      - id: squiggle
+        name: Squiggle
+      - id: sideboard
+        name: Sideboard Lamp
+      - id: bamboo
+        name: Bamboo Lights
+      - id: djbooth
+        name: DJ Booth
+      - id: couch
+        name: Dual Outlet - Couch
+        channels: [1, 2]
+
+    # Device ids toggled on brief single press (driven by single_filter)
+    single_plugs: [squiggle, sideboard, bamboo, couch]
+
+    # Device ids toggled on press-hold-release (driven by hold_filter)
+    hold_plugs: [djbooth]
+
+    single_filter: single-filter
+    hold_filter: hold-filter
+
     nodes:
-      - id: zigbee-state-squiggle
-        type: mqtt in
-        broker: mosquitto
-        topic: zigbee2mqtt/Squiggle
-        qos: 0
-
-      - id: zigbee-state-sideboard
-        type: mqtt in
-        broker: mosquitto
-        topic: zigbee2mqtt/Sideboard Lamp
-        qos: 0
-
-      - id: zigbee-state-bamboo
-        type: mqtt in
-        broker: mosquitto
-        topic: zigbee2mqtt/Bamboo Lights
-        qos: 0
-
-      - id: zigbee-state-djbooth
-        type: mqtt in
-        broker: mosquitto
-        topic: zigbee2mqtt/DJ Booth
-        qos: 0
-
-      - id: zigbee-state-couch
-        type: mqtt in
-        broker: mosquitto
-        topic: zigbee2mqtt/Dual Outlet - Couch
-        qos: 0
-
       - id: button-in
         type: mqtt in
         broker: mosquitto
@@ -100,73 +86,6 @@ flows:
           } catch (e) {}
           return null;
 
-      - id: plug-out-squiggle
-        type: mqtt out
-        broker: mosquitto
-        topic: zigbee2mqtt/Squiggle/set
-
-      - id: plug-out-sideboard
-        type: mqtt out
-        broker: mosquitto
-        topic: zigbee2mqtt/Sideboard Lamp/set
-
-      - id: plug-out-bamboo
-        type: mqtt out
-        broker: mosquitto
-        topic: zigbee2mqtt/Bamboo Lights/set
-
-      - id: plug-out-djbooth
-        type: mqtt out
-        broker: mosquitto
-        topic: zigbee2mqtt/DJ Booth/set
-
-      - id: couch-mapper
-        type: function
-        name: Toggle both outlets
-        code: |
-          msg.payload = { state_1: 'TOGGLE', state_2: 'TOGGLE' };
-          return msg;
-
-      - id: plug-out-couch
-        type: mqtt out
-        broker: mosquitto
-        topic: zigbee2mqtt/Dual Outlet - Couch/set
-
-      - id: text-squiggle
-        type: ui-text
-        group: Plugs
-        label: Squiggle
-        format: "{{msg.payload.state}}"
-        order: 1
-
-      - id: text-sideboard
-        type: ui-text
-        group: Plugs
-        label: Sideboard Lamp
-        format: "{{msg.payload.state}}"
-        order: 2
-
-      - id: text-bamboo
-        type: ui-text
-        group: Plugs
-        label: Bamboo Lights
-        format: "{{msg.payload.state}}"
-        order: 3
-
-      - id: text-djbooth
-        type: ui-text
-        group: Plugs
-        label: DJ Booth
-        format: "{{msg.payload.state}}"
-        order: 4
-
-      - id: text-couch
-        type: ui-text
-        group: Plugs
-        label: Dual Outlet - Couch
-        format: "{{msg.payload.state_1}} / {{msg.payload.state_2}}"
-        order: 6
-
       - id: permit-btn
         type: ui-button
         group: Plugs
@@ -175,20 +94,12 @@ flows:
         payload:
           value: true
           time: 60
-        order: 5
+        order: 9
 
       - id: mqtt-out
         type: mqtt out
         broker: mosquitto
 
     wires:
-      zigbee-state-squiggle: [text-squiggle]
-      zigbee-state-sideboard: [text-sideboard]
-      zigbee-state-bamboo: [text-bamboo]
-      zigbee-state-djbooth: [text-djbooth]
-      zigbee-state-couch: [text-couch]
       button-in: [single-filter, hold-filter]
-      single-filter: [plug-out-squiggle, plug-out-sideboard, plug-out-bamboo, couch-mapper]
-      couch-mapper: [plug-out-couch]
-      hold-filter: [plug-out-djbooth]
       permit-btn: [mqtt-out]