Move Redis PubSub config to runtime initialization

- Remove static Redis PubSub configuration from runtime.exs
- Add dynamic pubsub_config/0 function in application.ex
- Configure PubSub adapter based on cluster_enabled and REDIS_URL at startup
- Ensures proper initialization order for distributed deployments

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

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

config/runtime.exs

@@ -122,21 +122,6 @@ if config_env() == :prod do
 
   config :aprsme, :cluster_enabled, cluster_enabled
 
-  # Configure Redis PubSub when clustering is enabled
-  if cluster_enabled and System.get_env("REDIS_URL") do
-    config :aprsme, AprsmeWeb.Endpoint,
-      pubsub_server: Aprsme.PubSub,
-      pubsub: [
-        name: Aprsme.PubSub,
-        adapter: Phoenix.PubSub.Redis,
-        redis_pool_size: 10,
-        node_name: node(),
-        redis_options: [
-          url: System.get_env("REDIS_URL")
-        ]
-      ]
-  end
-
   # Optional: Set the default "from" email address
   config :aprsme,
     default_from_email: "w5isp@aprs.me"

lib/aprsme/application.ex

@@ -22,7 +22,7 @@ defmodule Aprsme.Application do
       # Start the Ecto repository
       Aprsme.Repo,
       # Start the PubSub system
-      {Phoenix.PubSub, name: Aprsme.PubSub},
+      pubsub_config(),
       # Start the rate limiter
       Aprsme.RateLimiter,
       # Start cache systems
@@ -162,4 +162,20 @@ defmodule Aprsme.Application do
 
     Logger.info("Automatic migrations disabled")
   end
+
+  defp pubsub_config do
+    cluster_enabled = Application.get_env(:aprsme, :cluster_enabled, false)
+    redis_url = System.get_env("REDIS_URL")
+
+    if cluster_enabled and redis_url do
+      {Phoenix.PubSub,
+       name: Aprsme.PubSub,
+       adapter: Phoenix.PubSub.Redis,
+       redis_pool_size: 10,
+       node_name: node(),
+       redis_options: [url: redis_url]}
+    else
+      {Phoenix.PubSub, name: Aprsme.PubSub}
+    end
+  end
 end