feat: add 5-channel relay GPIO outputs for HVAC control wiring

firmware/components/relays.yaml

@@ -1 +1,45 @@
-# placeholder — see task 3/4/5/6
+switch:
+  - platform: gpio
+    id: relay_fan
+    name: "Relay G — Fan"
+    pin:
+      number: GPIO11   # repurposed from TF card MOSI — Phase 1 tradeoff, see build notes
+      inverted: false   # set true if relay module is active-LOW
+    restore_mode: ALWAYS_OFF
+    icon: mdi:fan
+
+  - platform: gpio
+    id: relay_cool1
+    name: "Relay Y1 — Cool Stage 1"
+    pin:
+      number: GPIO12   # repurposed from TF card SCK
+      inverted: false
+    restore_mode: ALWAYS_OFF
+    icon: mdi:snowflake
+
+  - platform: gpio
+    id: relay_cool2
+    name: "Relay Y2 — Cool Stage 2"
+    pin:
+      number: GPIO13   # repurposed from TF card MISO
+      inverted: false
+    restore_mode: ALWAYS_OFF
+    icon: mdi:snowflake-variant
+
+  - platform: gpio
+    id: relay_heat1
+    name: "Relay W1 — Heat Stage 1"
+    pin:
+      number: GPIO15   # repurposed from RS485 TXD
+      inverted: false
+    restore_mode: ALWAYS_OFF
+    icon: mdi:fire
+
+  - platform: gpio
+    id: relay_heat2
+    name: "Relay W2 — Heat Stage 2"
+    pin:
+      number: GPIO16   # repurposed from RS485 RXD
+      inverted: false
+    restore_mode: ALWAYS_OFF
+    icon: mdi:fire-alert