Play every tab's preview straight into the master (#368)

Since #351 the tabs played their asset along its links in the Master
routing, as the game does. A song linked into a reverb bus was heard
through that bus while it was edited. A preview should sound like the
asset itself, so the tabs leave the Master routing out again.

- The Sound, Sound FX, Instrument, Pattern and Song tab play into the
  master. The sound FX of the asset still applies, and so does the
  master's own volume and FX.
- Inside a song its own routing of tracks and sends still counts.
- The game is unchanged: Play nodes go along the routing as before.

Tests:
- e2e 34 (melektaus-atx): ALL PASSED, 96 checks. The routing check
  now holds the mix of the two buses as before, and the Sound tab on
  the master with the bus silent.
- Counter-probe e2e: the Sound tab along the routing again, the
  routing check red.
- Gate (melektaus-atx): CHECK EXIT 0, 274 files, 4230 tests.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/viewport/music.ts

@@ -52,8 +52,8 @@ export class Music {
   readonly clips: PlannedClip[] = [];
 
   /**
-   * `output` is where what it plays goes (#351): along the routing of the pattern or song in the
-   * tab, so it sounds as it would in the game. The master where left out. `fx` is the sound FX of
+   * `output` is where what it plays goes (#351): the master where left out, as for the preview of
+   * a tab, which leaves the routing of its pattern or song out (#368). `fx` is the sound FX of
    * that pattern or song (#352), on the way there.
    */
   constructor(