feat: add oban dependency for background jobs

Add Oban ~> 2.18 with SQLite support (Oban.Engines.Lite) for durable
background job processing. Configure aggressive pruning (60s max_age)
to keep database lean, with a dedicated images queue.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

config/config.exs

@@ -73,6 +73,15 @@ config :logger, :default_formatter,
 # Use Jason for JSON parsing in Phoenix
 config :phoenix, :json_library, Jason
 
+# Oban configuration for background jobs
+config :simpleshop_theme, Oban,
+  engine: Oban.Engines.Lite,
+  repo: SimpleshopTheme.Repo,
+  plugins: [
+    {Oban.Plugins.Pruner, max_age: 60}
+  ],
+  queues: [images: 2]
+
 # Import environment specific config. This must remain at the bottom
 # of this file so it overrides the configuration defined above.
 import_config "#{config_env()}.exs"

config/test.exs

@@ -35,3 +35,6 @@ config :phoenix, :plug_init_mode, :runtime
 # Enable helpful, but potentially expensive runtime checks
 config :phoenix_live_view,
   enable_expensive_runtime_checks: true
+
+# Use inline testing mode for Oban
+config :simpleshop_theme, Oban, testing: :inline