chore(qt): ship the binary as qbz, and log the first MPRIS metadata push

The artifact is now `target/<profile>/qbz` (owner, 2026-08-04). The package
stays `qbz-qt`, so `cargo build -p qbz-qt` is unchanged.

⚠ `crates/qbz` — the Slint binary — declares the SAME bin name and shares
this workspace's target dir, so both write `target/<profile>/qbz` and the
last build wins. Survivable only because the Slint binary is never built in
this worktree (the qbz-ui 20-30 GB wall); if it ever is, a smoke against
"the wrong qbz" is silent. Written into Cargo.toml beside the name.

The MPRIS line exists because "Plasma sees nothing" has two very different
causes — the player never registered, or it registered and no metadata was
ever pushed — and the log could not tell them apart. It settled that
question the same day: the owner's log shows `[mpris] metadata pushed:
Holy Diver — Dio (350s)`, so the port's half works and what remains is
desktop-side.

cc

scripts/qt-run.sh

@@ -123,7 +123,7 @@ if [[ "${DEBUG:-0}" == 1 ]]; then
 else
   PROFILE=release; PROFILE_ARGS=(--release)
 fi
-BIN="crates/target/${PROFILE}/qbz-qt"
+BIN="crates/target/${PROFILE}/qbz"
 
 # --- ONE BUILD AT A TIME, BOX-WIDE ------------------------------------------
 # Not paranoia: a Slint `qbz-ui` rustc in another worktree peaks 20-30 GB on a