Describe the embedded take of a song (#355)

A recorded take now lives inside its song instead of the Assets
panel. Songs explains what that means for playing, editing and
deleting.

- Songs: new section Embedded assets, the item menu with Open,
  Make project asset and Embed a copy, and the take named Take 1.
- Development: 1885 checks.

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

Development.md

@@ -19,7 +19,7 @@ php tests/php/accounts.test.php                               # the API's accoun
 php tests/php/snapshots.test.php                              # the snapshot store (#231), the same way
 php tests/php/releases.test.php                               # the release store (#266), the same way
 php tests/php/files.test.php                                  # uploaded files in a folder per account (#344), the same way
-node tools/seed-e2e.mjs && node tools/e2e.mjs                 # 1884 editor checks, screenshots in /tmp/gm-e2e-*.png
+node tools/seed-e2e.mjs && node tools/e2e.mjs                 # 1885 editor checks, screenshots in /tmp/gm-e2e-*.png
 GM_STEPS=20 node tools/e2e.mjs                                # or 1-12, or 6,20 — a subset while working on one step
 ./e2e.sh start [GM_STEPS]                                     # the same run detached, see below
 ./e2e.sh status                                               # live progress, or the last run's result

Songs.md

@@ -88,7 +88,7 @@ right-click menu, not from the inspector.
 | Click on nothing in the lanes | Picks the song itself. |
 | Click a head | Picks its track. |
 | `Shift`-click an item | Adds it to the pick or takes it out. Dragged on with `Shift`, it is added and moved or sized off the grid instead. |
-| Right-click an item | Opens its menu: *Delete* deletes it, or every picked item where it is one of them. |
+| Right-click an item | Opens its menu: *Open* opens what it plays (as a double-click does), *Make project asset* or *Embed a copy* (see [Embedded assets](#embedded-assets)), and *Delete* deletes it, or every picked item where it is one of them. |
 | Double-click a pattern item | Opens the pattern in the Pattern tab, with what the song plays around the round clicked into as [ghost notes](Patterns#ghost-notes-from-the-song). |
 | Double-click a sound item | Opens the sound in the Sound tab (#352). |
 | Click **M** or **S** in a head | Mutes or solos the track. |
@@ -199,8 +199,10 @@ names of the inputs show once recording has been allowed, and the browser keeps
   track clicked last (else under the last one); the lanes take no edits, only a middle-drag pans.
   The meter next to the input shows its level, red near full scale.
 - **Stop**, **Play** or `Space` keep it: it goes up as a WAV file (one channel, 16 bits, at the
-  rate of the sound device), becomes the sound *Song – Take 1*, 2 … and lies on its track from where
-  playing started. Sound, track and item are one undo step. `Esc` throws it away, nothing goes up.
+  rate of the sound device), becomes the sound *Take 1*, 2 … that the song keeps to itself (see
+  [Embedded assets](#embedded-assets), numbered per song) and lies on its track from where playing
+  started. Sound, track and item are one undo step. `Esc` throws it away, nothing goes up. Should the
+  song be deleted while the take goes up, the take becomes a project sound instead.
 - It is cut so that what was played along to the song lies where it was heard: the delay of the
   output and of the input, as far as the browser tells them, are taken off. What is left over can be
   moved with `Alt`-drag. The browser's echo cancelling, noise filter and automatic gain are off;
@@ -209,6 +211,29 @@ names of the inputs show once recording has been allowed, and the browser keeps
   itself. If the upload fails, a box offers *Retry*, *Download WAV* and *Discard*.
 - Opening another project throws a take away; showing another song or playing a pattern keeps it.
 
+## Embedded assets
+
+A sound, a pattern or a sound FX can belong to one song instead of the project (#355). A take is
+one. It is edited like any other: a double-click on its item opens it in its tab, where *Reverse*,
+the cut and the fades work as always, and the tab's title has the song's name in front of its own.
+But it has no row in the Assets panel, no picker offers it (not the inspector, not a node), and
+its name only has to be free within the song.
+
+- **One user.** An embedded asset is used by exactly one place of its song: an item, a track or the
+  song itself. A split, `Ctrl+D` and a paste give every new item a copy of its own, so setting one
+  half of a split take to *Reverse* leaves the other half as it was. The audio file is not copied:
+  files are stored by their content.
+- **It goes with its user.** Deleting the item, its track or the song deletes the embedded asset
+  in the same undo step. A copied item keeps it in the clipboard, so a paste after the delete brings
+  it back. *Duplicate* on the song copies everything it keeps to itself.
+- A click on its name in the inspector lights up its song in the Assets panel.
+- In the Sound tab of an embedded sound the rows *Loop* and *Bus* are left out: in a song an item
+  repeats its sound as long as it is, and the track decides where it goes.
+- **Make project asset** (the item's menu) turns an embedded asset into an ordinary one; a name the
+  project has already gets a number. **Embed a copy** goes the other way: the item plays a copy of
+  its project asset that only the song has, to bend without touching the rest.
+- A project file whose song is gone keeps such an asset as a project asset.
+
 ## Playing one in a game
 
 **Play song** plays a song at its tempo, its tracks with the volume, pan, mute and solo they have