docs(player): allocate UR-074/DR-162 for the streaming bitrate cap

The feature shipped tagged against DR-160, which a parallel session had
claimed for picture-in-picture in the meantime. Renumbered to DR-162
across the Rust and frontend TRACES comments (the PiP tags in
VideoPlayer.svelte, pictureInPicture.ts and nativeVideo.ts keep DR-160)
and regenerated bindings.ts.

Adds the requirement rows the tags point at: UR-074 for the user need, and
DR-162 covering why the cap has to reach the PlaybackInfo negotiation and
not only the transcode URL, why the ceiling is process-wide, and why the
Settings default persists while the in-player override does not. Notes
that this gives UR-070 its resume-at-the-same-point mechanism while the
server-offered rendition list that requirement also asks for stays
proposed. UT-156/157 record what the tests pin.

docs/specs/streaming-bitrate-cap.md carries the layer assignment — the
step definitions, the video/audio split, the resolution pairing and the
reload decision are all Rust; the frontend holds a serde token and the
labels it was handed.

TRACES: UR-074 | DR-162 | UT-156, UT-157

src/lib/components/player/VideoPlayer.svelte

@@ -246,7 +246,7 @@
 
   // Streaming bandwidth ceiling. The ladder and the current value both come from
   // Rust — the frontend never encodes what a step means.
-  // TRACES: UR-074 | DR-160
+  // TRACES: UR-074 | DR-162
   let showQualityMenu = $state(false);
   let streamingQualities = $state<[StreamingQuality, string, string][]>([]);
   let selectedQuality = $state<StreamingQuality>("original");
@@ -653,7 +653,7 @@
   // flips the component into HTML5 mode and breaks native seeking, and nothing
   // about playback waits on this list.
   //
-  // TRACES: UR-074 | DR-160
+  // TRACES: UR-074 | DR-162
   onMount(() => {
     Promise.all([
       commands.playerGetStreamingQualities(),
@@ -1929,7 +1929,7 @@
    * only supplies the position to resume at and reverts the selection if the
    * switch fails.
    *
-   * TRACES: UR-074 | DR-160
+   * TRACES: UR-074 | DR-162
    */
   async function selectQuality(quality: StreamingQuality) {
     showQualityMenu = false;
@@ -2354,7 +2354,7 @@
           </div>
         {/if}
 
-        <!-- Streaming quality (bandwidth ceiling). TRACES: UR-074 | DR-160 -->
+        <!-- Streaming quality (bandwidth ceiling). TRACES: UR-074 | DR-162 -->
         {#if streamingQualities.length > 0}
           <div class="relative">
             <button