Fix dashboard MQTT connection and remove simulation code

- Replace SimpleMqtt simulation with real MqttSubscriber
- Fix String.split bug when handling MQTT topic parsing
- Use hostname-based client ID to avoid MQTT client conflicts
- Add process management tools (hivemind, just) to development environment

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

dashboard/lib/dashboard/mqtt_subscriber.ex

@@ -19,17 +19,27 @@ defmodule Dashboard.MqttSubscriber do
 
   @impl true
   def init(_opts) do
-    # Start MQTT connection in a supervised way
-    {:ok, _pid} = Tortoise.Supervisor.start_child(
-      :dashboard_mqtt,
-      client_id: :dashboard_mqtt,
+    # Start MQTT connection directly with hostname-based client ID to avoid conflicts
+    {:ok, hostname} = :inet.gethostname()
+    client_id = "systant-dashboard-#{hostname}"
+    connection_opts = [
+      client_id: client_id,
       server: {Tortoise.Transport.Tcp, host: "mqtt.home", port: 1883},
       handler: {__MODULE__, []},
       subscriptions: [{"systant/+/stats", 0}]
-    )
-    
-    Logger.info("Dashboard MQTT subscriber started")
-    {:ok, %{hosts: %{}}}
+    ]
+
+    case Tortoise.Connection.start_link(connection_opts) do
+      {:ok, _pid} ->
+        Logger.info("Dashboard MQTT subscriber connected successfully")
+        {:ok, %{hosts: %{}}}
+      {:error, {:already_started, _pid}} ->
+        Logger.info("Dashboard MQTT connection already exists, reusing")
+        {:ok, %{hosts: %{}}}
+      {:error, reason} ->
+        Logger.error("Failed to connect to MQTT broker: #{inspect(reason)}")
+        {:stop, reason}
+    end
   end
 
   @impl true
@@ -43,11 +53,19 @@ defmodule Dashboard.MqttSubscriber do
   end
 
   # Tortoise handler callbacks
-  def connection(_status, _state), do: []
-  def subscription(_status, _topic, _state), do: []
+  def connection(status, state) do
+    Logger.info("MQTT connection status: #{status}")
+    {:ok, state}
+  end
+  
+  def subscription(status, topic, state) do
+    Logger.info("MQTT subscription status for #{topic}: #{status}")
+    {:ok, state}
+  end
   
   def handle_message(topic, payload, _state) do
-    case String.split(topic, "/") do
+    topic_parts = if is_binary(topic), do: String.split(topic, "/"), else: topic
+    case topic_parts do
       ["systant", hostname, "stats"] ->
         case Jason.decode(payload) do
           {:ok, data} ->
@@ -74,5 +92,6 @@ defmodule Dashboard.MqttSubscriber do
     {:noreply, %{state | hosts: updated_hosts}}
   end
 
+  @impl true
   def terminate(_reason, _state), do: []
 end