add dynamic routes plug and simplify router

Dynamic prefix rewriting for custom URL prefixes:
- DynamicRoutes plug rewrites /p/123 to /products/123
- 301 redirects from canonical to custom prefix
- Router simplified to 3 catch-all routes
- LiveSandboxHook for test process ownership

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

lib/berrypod_web/endpoint.ex

@@ -13,8 +13,8 @@ defmodule BerrypodWeb.Endpoint do
   ]
 
   socket "/live", Phoenix.LiveView.Socket,
-    websocket: [connect_info: [session: @session_options]],
-    longpoll: [connect_info: [session: @session_options]]
+    websocket: [connect_info: [:user_agent, session: @session_options]],
+    longpoll: [connect_info: [:user_agent, session: @session_options]]
 
   # In prod, image variants and mockups live on the persistent volume
   # rather than inside the ephemeral release directory.
@@ -50,6 +50,11 @@ defmodule BerrypodWeb.Endpoint do
     plug Tidewave, allow_remote_access: true
   end
 
+  # Enable sandbox for LiveView tests (allows LV processes to share test DB connection)
+  if Application.compile_env(:berrypod, :env) == :test do
+    plug Phoenix.Ecto.SQL.Sandbox
+  end
+
   # Code reloading can be explicitly enabled under the
   # :code_reloader configuration of your endpoint.
   if code_reloading? do
@@ -76,5 +81,6 @@ defmodule BerrypodWeb.Endpoint do
   plug Plug.Head
   plug Plug.Session, @session_options
   plug BerrypodWeb.Plugs.Redirects
+  plug BerrypodWeb.Plugs.DynamicRoutes
   plug BerrypodWeb.Plugs.BrokenUrlTracker, router: BerrypodWeb.Router
 end