chore(traceability): shift this branch's ids clear of master's

Master allocated DR-224 and UT-211 while this branch was in flight — the third
collision on this work. Everything here moves up by one: DR-224..236 become
DR-225..237, UT-211..213 become UT-212..214. UR-079, UR-080 and IR-033 were
still free and are unchanged.

Mechanical, and matched on each row's own text rather than on its number, so a
row cannot be shifted twice or the wrong one caught. Master's DR-224 (the
background-audio toggle) and UT-211 are untouched.

docs/specs/read-through-media-cache.md

@@ -9,7 +9,7 @@ DR-124, DR-125.
 
 **DR-121 has shipped and left this spec.** The player quality selector, the
 per-playback bitrate ceiling, and the backend-owned stream decision it needed
-were built as *backend-owned stream selection* (DR-224 … DR-227) and are
+were built as *backend-owned stream selection* (DR-225 … DR-228) and are
 described in
 [01-rust-backend.md](../architecture/01-rust-backend.md#stream-selection) and
 [03-data-flow.md](../architecture/03-data-flow.md#video-stream-selection-flow).
@@ -77,7 +77,7 @@ frontend stores the user's *choice*; Rust decides what that choice resolves to.
 
 ### DR-121 — moved out (shipped)
 
-Bitrate selection in the player shipped as DR-224 … DR-227; see
+Bitrate selection in the player shipped as DR-225 … DR-228; see
 [01-rust-backend.md](../architecture/01-rust-backend.md#stream-selection).
 
 The one constraint here that the capture work still has to respect: a quality