add URL redirects with ETS-cached plug, broken URL tracking, and admin UI

Redirects context with redirect/broken_url schemas, chain flattening,
ETS cache for fast lookups in the request pipeline. BrokenUrlTracker
plug logs 404s. Auto-redirect on product slug change via upsert_product
hook. Admin redirects page with active/broken tabs, manual create form.
RedirectPrunerWorker cleans up old broken URLs. 1227 tests passing.

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

lib/berrypod_web/plugs/broken_url_tracker.ex

@@ -0,0 +1,34 @@
+defmodule BerrypodWeb.Plugs.BrokenUrlTracker do
+  @moduledoc """
+  Wraps the router to record 404s in the broken URLs table.
+
+  Works in dev mode too — Plug.Debugger intercepts exceptions before
+  error templates render, so we catch NoRouteError here, record it,
+  then re-raise so the normal error handling continues.
+  """
+
+  @behaviour Plug
+
+  def init(opts) do
+    router = Keyword.fetch!(opts, :router)
+    router_opts = router.init([])
+    {router, router_opts}
+  end
+
+  def call(conn, {router, router_opts}) do
+    router.call(conn, router_opts)
+  rescue
+    e in Phoenix.Router.NoRouteError ->
+      unless static_path?(conn.request_path) do
+        Berrypod.Redirects.record_broken_url(conn.request_path, 0)
+      end
+
+      reraise e, __STACKTRACE__
+  end
+
+  defp static_path?(path) do
+    String.starts_with?(path, "/assets/") or
+      String.starts_with?(path, "/images/") or
+      String.starts_with?(path, "/favicon")
+  end
+end

lib/berrypod_web/plugs/redirects.ex

@@ -0,0 +1,66 @@
+defmodule BerrypodWeb.Plugs.Redirects do
+  @moduledoc """
+  Plug that handles URL normalisation and custom redirects.
+
+  Three concerns in one pass:
+  1. Trailing slash removal (/products/foo/ → /products/foo)
+  2. Case normalisation for shop paths (/Products/Foo → /products/foo)
+  3. Custom redirect lookup from the redirects table (ETS-cached)
+
+  All redirects preserve query params.
+  """
+
+  import Plug.Conn
+  alias Berrypod.Redirects
+
+  # Only case-normalise paths under these prefixes (SEO-relevant shop routes).
+  # Paths with tokens, API keys, or other case-sensitive segments are excluded.
+  @lowercase_prefixes ~w(/products /collections /about /delivery /privacy /terms /search /cart /contact)
+
+  def init(opts), do: opts
+
+  def call(conn, _opts) do
+    path = conn.request_path
+    stripped = strip_trailing_slash(path)
+
+    cond do
+      # Trailing slash — redirect to canonical form
+      stripped != path ->
+        redirect_to(conn, stripped, 301)
+
+      # Case mismatch on a shop path — redirect to lowercase
+      lowercase_path?(path) and String.downcase(path) != path ->
+        redirect_to(conn, String.downcase(path), 301)
+
+      # Check redirect table (ETS-cached)
+      :else ->
+        case Redirects.lookup(path) do
+          {:ok, redirect} ->
+            Redirects.increment_hit_count(redirect)
+            redirect_to(conn, redirect.to_path, redirect.status_code)
+
+          :not_found ->
+            conn
+        end
+    end
+  end
+
+  defp lowercase_path?(path) do
+    Enum.any?(@lowercase_prefixes, &String.starts_with?(String.downcase(path), &1))
+  end
+
+  defp redirect_to(conn, target, status_code) do
+    location = append_query(target, conn.query_string)
+
+    conn
+    |> put_resp_header("location", location)
+    |> send_resp(status_code, "")
+    |> halt()
+  end
+
+  defp strip_trailing_slash("/"), do: "/"
+  defp strip_trailing_slash(path), do: String.trim_trailing(path, "/")
+
+  defp append_query(path, ""), do: path
+  defp append_query(path, qs), do: "#{path}?#{qs}"
+end