feat(editor): F4.6a simulation mode and a computer's desktop

Java's mode buttons start and stop the room, now in a worker of the
editor's page (LocalSimHost), with Java's speed slider. While the
simulation runs the design is locked as in Java: no palette, no sheet,
nothing moves, no undo. Cables that carry a frame light up in Java's
green, and a tap on a computer opens its desktop: Java's title, the
software installation first, then the installed programs in the order
of Java's list for the language, a taskbar with the network icon and
the network as the simulation runs it. The room sends that over a new
topic, node:<id>. Desktops stay over a return to the design and show
again at the next start. The programs' windows follow from F4.6b.

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

packages/protocol/test/sim.test.ts

@@ -35,15 +35,15 @@ describe("a client's messages", () => {
   });
 
   it('knows its topics', () => {
-    expect(['activity', 'trace:x', 'app:n/gnutella', 'app:n/webBrowser'].every(isTopic)).toBe(true);
-    expect(['', 'trace:', 'app:/terminal', 'app:n/', 'app:n/terminal/x', 'node:n', 7].some(isTopic)).toBe(false);
+    expect(['activity', 'trace:x', 'app:n/gnutella', 'app:n/webBrowser', 'node:n'].every(isTopic)).toBe(true);
+    expect(['', 'trace:', 'app:/terminal', 'app:n/', 'app:n/terminal/x', 'node:', 'node:n/x', 'nodes:n', 7].some(isTopic)).toBe(false);
   });
 });
 
 describe("a host's messages", () => {
   it('reads each kind, and names an unknown one', () => {
     for (const kind of HOST_MESSAGE_KINDS) expect('message' in parseHostMessage({ v: 1, kind })).toBe(true);
-    expect(parseHostMessage({ v: 1, kind: 'node' })).toEqual({ error: { code: 'unknownKind', detail: 'kind node' } });
+    expect(parseHostMessage({ v: 1, kind: 'nodes' })).toEqual({ error: { code: 'unknownKind', detail: 'kind nodes' } });
     expect(parseHostMessage({ v: 0, kind: 'state' })).toEqual({ error: { code: 'badVersion', detail: 'version 0' } });
   });
 });