Route sounds, songs and buses in one Master routing graph (#351)

A project bus could only go into one other bus, and a sound, an
instrument, a pattern or a song into exactly one bus. A shared reverb
needs a sound to go there in part and on dry at the same time. Instead
of a list of sends on every asset, the project gets one routing graph
like the routing of a song (#350), one level up.

- Menu -> Master routing opens a tab with one graph per project. It has
  a node per sound, instrument, pattern, song and bus, named after its
  asset, and one Master. Embedded assets have none, their song routes
  them.
- The nodes follow the assets. Every edit settles the routing in the
  same undo step (KeepRoutingCommand), so an undone delete brings the
  links of its asset back. A new asset gets a node and a link to the
  master. What went only into a deleted bus goes to the master.
- New nodes start in three columns: what plays, the buses, and the
  master a row above, so no link into it runs behind a bus.
- Links are sends: -60 to +12 dB, and a Mode on links out of a bus or a
  song. Out of a sound, an instrument or a pattern a link always takes
  the sound after its volume and FX. Loops are refused.
- A node without a link is silent and says "Goes nowhere".
- The rows Bus and Into are gone. Play nodes with a picked bus still
  overrule the routing.
- A click on a node shows its asset in the inspector, the Master shows
  the master volume and sound FX. A double click opens the asset's tab.
- The graph lives in project.routing and is held to the assets when a
  project is read, but nothing is added there. The editor adds the
  nodes when it opens a project. An asset without a node plays on the
  master, so old projects sound as before without a migration.
- In the mix an asset with one link at 0 dB goes straight into that bus.
  A sound or instrument with more gets a bus of its own with the sends.
  A pattern or song sends from the master of its playing, which is
  where its Mode taps. Buses of the mix can have sends now too.

Found:

- The check "the scheduler plans a looped bar" in e2e 34 wobbles. It
  failed in 2 of 5 runs here and in CI task 580 at 490fcba, before
  this change. HEAD passed it 2 of 2. Not fixed here.

Tests:

- Unit master-routing (new, 10), sound-library (2 new), buses
  rewritten onto the routing, 5 lists without the Bus row. 5 counter
  checks red.
- e2e 34 (melektaus-atx): ALL PASSED, 93 checks (3 new, 2 rewritten).
  Counter check with the Sound tab ignoring the routing: the routing
  check red.
- Gate (melektaus-atx): CHECK EXIT 0, 273 files, 4225 tests.

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

src/core/store/serialize.ts

@@ -25,7 +25,8 @@ import { heldPatternNotes } from '../music/pattern';
 import { isEmbeddable } from '../music/embedded';
 import { heldSongItems, heldSongTracks } from '../music/song';
 import { heldSend, heldSongGraph } from '../music/routing';
-import { isSongRoutingDef } from '../music/routingNodes';
+import { isMasterRoutingDef, isSongRoutingDef } from '../music/routingNodes';
+import { heldRouting } from '../music/projectRouting';
 import { heldLoop, type LoopRange } from '../music/sequence';
 import { isKeyInterpolation, normalizeKeys } from '../model/animation';
 import type {
@@ -340,6 +341,7 @@ export function deserializeProject(raw: unknown, fallbackId = ''): Project {
     renderLayers: renderLayersOf(r),
     masterVolume: masterVolumeOf(r),
     masterFx: masterFxOf(r),
+    routing: heldRouting(normalizeGraph(r.routing, isMasterRoutingDef), assets, false),
     symbolScale: symbolScaleOf(r),
     playFrom: playFromOf(r),
     whilePlaying: whilePlayingOf(r),