fix(web): drop back button from movie and series pages (#229)

The rail, browser back, and Esc already cover navigation — the back
button was a third way to do what two other things already do, and it
cost the page its first line.

- Remove #movie-back and #series-back buttons and their event listeners
- Focus lands on the title element (tabindex=-1) instead of the removed
  button on open
- TV releases back button is untouched
- Hero banner now meets the rail with zero top padding on movie/series
- Esc and parent-route behaviour unchanged
- Deep link fallback for TV releases uses #nav-library instead of the
  removed #series-back

web/index.html

@@ -218,10 +218,7 @@
     -->
 
     <main class="deck" id="movie" hidden aria-label="movie detail">
-      <header class="releases-head">
-        <button type="button" class="control" id="movie-back">back</button>
-        <p class="deck-status readout" id="movie-status" role="status" hidden></p>
-      </header>
+      <p class="deck-status readout" id="movie-status" role="status" hidden></p>
 
       <section class="module movie-hero" id="movie-hero" aria-label="title metadata">
         <div class="movie-body">
@@ -470,10 +467,7 @@
     -->
 
     <main class="deck releases" id="series" hidden aria-label="series detail">
-      <header class="releases-head">
-        <button type="button" class="control" id="series-back">back</button>
-        <p class="deck-status readout" id="series-status" role="status" hidden></p>
-      </header>
+      <p class="deck-status readout" id="series-status" role="status" hidden></p>
 
       <section class="module movie-hero" id="series-hero" aria-label="title metadata">
         <div class="movie-body">