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/routes/settings/+page.svelte

@@ -68,7 +68,7 @@
 
   // Bandwidth ceilings offered by the streaming-quality picker, as
   // [variant, label, detail] — the numbers behind each step are Jellyfin
-  // encoding vocabulary, so Rust serves the list. TRACES: UR-074 | DR-160
+  // encoding vocabulary, so Rust serves the list. TRACES: UR-074 | DR-162
   let streamingQualities = $state<[StreamingQuality, string, string][]>([]);
 
   // Download/caching behaviour, incl. the WiFi-only gate (UR-053).
@@ -340,7 +340,7 @@
     persistVideo();
   }
 
-  /** TRACES: UR-074 | DR-160 */
+  /** TRACES: UR-074 | DR-162 */
   function handleStreamingQualityChange(quality: StreamingQuality) {
     videoSettings.streamingQuality = quality;
     persistVideo();
@@ -698,7 +698,7 @@
 
         <!-- Streaming quality: the bandwidth ceiling every video stream is
              opened against. The steps and their labels come from Rust.
-             TRACES: UR-074 | DR-160 -->
+             TRACES: UR-074 | DR-162 -->
         <div class="bg-[var(--color-surface)] rounded-lg p-6 mt-4">
           <h3 class="text-xl font-semibold text-white">Streaming Quality</h3>
           <p class="text-sm text-gray-400 mt-1 mb-4">