feat: add Redis password authentication support

Add REDIS_PASSWORD environment variable support to both Phoenix.PubSub.Redis
and Exq background job processor. Password is optional - if not set, connects
without authentication.

Changes:
- application.ex: Add password to PubSub Redis config if REDIS_PASSWORD is set
- exq_supervisor.ex: Add password to Exq Redis config if REDIS_PASSWORD is set

Required for connecting to Proxmox-hosted Redis with authentication.

lib/towerops/application.ex

@@ -117,6 +117,14 @@ defmodule Towerops.Application do
       node_name: node()
     ]
 
+    # Add password if configured
+    base_opts =
+      case System.get_env("REDIS_PASSWORD") do
+        nil -> base_opts
+        "" -> base_opts
+        password -> Keyword.put(base_opts, :password, password)
+      end
+
     # Add resilience options for better reconnection handling
     resilience_opts = [
       # Redix connection options for better resilience

lib/towerops/exq_supervisor.ex

@@ -65,7 +65,7 @@ defmodule Towerops.ExqSupervisor do
   end
 
   defp build_exq_config(redis_config) do
-    [
+    base_config = [
       name: Exq,
       host: Keyword.get(redis_config, :host, "localhost"),
       port: Keyword.get(redis_config, :port, 6379),
@@ -96,5 +96,12 @@ defmodule Towerops.ExqSupervisor do
         socket_opts: [keepalive: true]
       ]
     ]
+
+    # Add password if configured
+    case System.get_env("REDIS_PASSWORD") do
+      nil -> base_config
+      "" -> base_config
+      password -> Keyword.put(base_config, :password, password)
+    end
   end
 end