Fix startup issues with Redis and shutdown handlers

- Delay DeviceCache initial load by 1 second to allow Redis connections
- Move shutdown handlers to end of supervision tree
- This prevents shutdown handlers from interfering with startup failures

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

lib/aprsme/application.ex

@@ -24,10 +24,6 @@ defmodule Aprsme.Application do
       # Start the PubSub system
       pubsub_config(),
       # Start Redis-based rate limiter and caches (only if Redis is available)
-      # Start signal handler for OS signals
-      Aprsme.SignalHandler,
-      # Start shutdown handler for graceful shutdowns
-      Aprsme.ShutdownHandler,
       # Start circuit breaker
       Aprsme.CircuitBreaker,
       # Start device cache manager
@@ -55,6 +51,15 @@ defmodule Aprsme.Application do
     ]
 
     children = children ++ redis_children()
+
+    # Add shutdown handlers at the end, after everything else is started
+    children =
+      children ++
+        [
+          Aprsme.SignalHandler,
+          Aprsme.ShutdownHandler
+        ]
+
     children = maybe_add_cluster_components(children)
     children = maybe_add_is_supervisor(children, Application.get_env(:aprsme, :env))
     children = maybe_add_aprs_connection(children, Application.get_env(:aprsme, :env))

lib/aprsme/device_cache.ex

@@ -53,18 +53,26 @@ defmodule Aprsme.DeviceCache do
 
   @impl true
   def init(_) do
+    # Delay initial load to allow Redis connections to establish
+    Process.send_after(self(), :initial_load, 1_000)
+
+    {:ok, %{initial_load_done: false}}
+  end
+
+  @impl true
+  def handle_info(:initial_load, state) do
     # Load devices on startup
     case load_devices_into_cache() do
       :ok ->
         # Schedule periodic refresh
         Process.send_after(self(), :refresh_cache, @refresh_interval)
+        {:noreply, %{state | initial_load_done: true}}
 
       :error ->
         # If initial load failed, retry sooner
-        Process.send_after(self(), :refresh_cache, 5_000)
+        Process.send_after(self(), :initial_load, 5_000)
+        {:noreply, state}
     end
-
-    {:ok, %{}}
   end
 
   @impl true