add observability: LiveDashboard in prod, error tracking, JSON logging

- Move LiveDashboard to /admin/dashboard behind session auth (all envs)
- Add ErrorTracker at /admin/errors for auto-captured exceptions
- Add Oban job and LiveView metrics to telemetry module
- Add logger_json for structured JSON logs in production
- Enable os_mon for CPU/disk/memory in LiveDashboard OS Data tab
- Extend logger metadata with oban_worker and oban_queue fields

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

lib/simpleshop_theme_web/router.ex

@@ -2,6 +2,8 @@ defmodule SimpleshopThemeWeb.Router do
   use SimpleshopThemeWeb, :router
 
   import SimpleshopThemeWeb.UserAuth
+  import Phoenix.LiveDashboard.Router
+  import ErrorTracker.Web.Router
 
   pipeline :browser do
     plug :accepts, ["html"]
@@ -89,19 +91,19 @@ defmodule SimpleshopThemeWeb.Router do
     post "/stripe", StripeWebhookController, :handle
   end
 
-  # Enable LiveDashboard and Swoosh mailbox preview in development
-  if Application.compile_env(:simpleshop_theme, :dev_routes) do
-    # If you want to use the LiveDashboard in production, you should put
-    # it behind authentication and allow only admins to access it.
-    # If your application does not have an admins-only section yet,
-    # you can use Plug.BasicAuth to set up some basic authentication
-    # as long as you are also using SSL (which you should anyway).
-    import Phoenix.LiveDashboard.Router
+  # LiveDashboard and ErrorTracker behind admin auth (available in all environments)
+  scope "/admin" do
+    pipe_through [:browser, :require_authenticated_user]
 
+    live_dashboard "/dashboard", metrics: SimpleshopThemeWeb.Telemetry
+    error_tracker_dashboard("/errors")
+  end
+
+  # Dev-only routes (mailbox preview, error previews)
+  if Application.compile_env(:simpleshop_theme, :dev_routes) do
     scope "/dev" do
       pipe_through :browser
 
-      live_dashboard "/dashboard", metrics: SimpleshopThemeWeb.Telemetry
       forward "/mailbox", Plug.Swoosh.MailboxPreview
 
       # Preview error pages

lib/simpleshop_theme_web/telemetry.ex

@@ -75,6 +75,24 @@ defmodule SimpleshopThemeWeb.Telemetry do
           "The time the connection spent waiting before being checked out for the query"
       ),
 
+      # Oban job metrics
+      summary("oban.job.stop.duration",
+        tags: [:worker],
+        unit: {:native, :millisecond}
+      ),
+      counter("oban.job.stop.duration", tags: [:worker]),
+      counter("oban.job.exception.duration", tags: [:worker]),
+
+      # LiveView metrics
+      summary("phoenix.live_view.mount.stop.duration",
+        tags: [:view],
+        unit: {:native, :millisecond}
+      ),
+      summary("phoenix.live_view.handle_event.stop.duration",
+        tags: [:event],
+        unit: {:native, :millisecond}
+      ),
+
       # VM Metrics
       summary("vm.memory.total", unit: {:byte, :kilobyte}),
       summary("vm.total_run_queue_lengths.total"),