feat(arr): render subtitle settings in /settings

Adds wanted languages, translation engine (restricted to
available_engines), remote-command timeout, and an ordered
enable/disable list per provider with daily budgets, wired to
the existing GET/PUT /api/settings/subtitles from #198.

web/index.html

@@ -468,6 +468,17 @@
         </p>
         <ul class="deck-rows" id="rows-policies"></ul>
       </section>
+
+      <section class="deck-group" id="group-subtitles" hidden aria-labelledby="label-settings-subtitles">
+        <header class="deck-head">
+          <h3 class="deck-label" id="label-settings-subtitles">subtitles</h3>
+        </header>
+        <p class="queue-note readout dim">
+          provider credentials, translator keys and the remote-command template
+          live in config/env (§10) and are never shown here.
+        </p>
+        <div id="subtitles-body"></div>
+      </section>
     </main>
 
     <!--