refactor(web): drop cast from title detail

DESIGN.md §9.6 no longer carries cast (#163). Removes the cast
sections, the MetadataCastMember schema and field from both metadata
responses, and every .cast-* rule. arr-meta keeps CastMember and the
credits append; the TMDB call is unchanged.

web/index.html

@@ -203,8 +203,7 @@
     metadata response's own key (no second call); TMDB, IMDb and Rotten
     Tomatoes sit beside it — RT is a search URL built here, never a resolved
     page. LIBRARY controls follow on their own row: wanted, blocked, root,
-    then search indexers and remove. CAST is the top 10 billed, each photo
-    linking out to that person's TMDB page. ON DISK lists imported files
+    then search indexers and remove. ON DISK lists imported files
     with ffprobe attribute tags and any §5.7 waiver, worded honestly. The
     §9.3 deck closes the page unchanged — buckets, chips, score heat and
     rejection rules untouched; /movies/{id}/releases lands here with the
@@ -271,13 +270,6 @@
         <div class="remove-panel" id="remove-panel" hidden></div>
       </section>
 
-      <section class="deck-group" id="movie-cast" hidden aria-labelledby="label-cast">
-        <header class="deck-head">
-          <h3 class="deck-label" id="label-cast">cast</h3>
-        </header>
-        <ul class="cast-grid" id="rows-cast"></ul>
-      </section>
-
       <section class="deck-group" id="movie-files" hidden aria-labelledby="label-disk">
         <header class="deck-head">
           <h3 class="deck-label" id="label-disk">on disk</h3>
@@ -428,13 +420,6 @@
         </div>
       </section>
 
-      <section class="deck-group" id="series-cast" hidden aria-labelledby="label-series-cast">
-        <header class="deck-head">
-          <h3 class="deck-label" id="label-series-cast">cast</h3>
-        </header>
-        <ul class="cast-grid" id="rows-series-cast"></ul>
-      </section>
-
       <ul class="deck-rows seasons" id="rows-seasons"></ul>
     </main>