feat(maestro): wire React app as sole web entry point

Deletes the vanilla shell and mounts App.tsx on #root. main.ts and the
23 views it drove are gone; App.tsx composes the ported components —
sidebar, multi-view, command bar, spawn modal, help and restart
overlays, daemon link, drawer — around the catalog and layout stores.

The pure parts of four deleted modules moved next to the components
that still use them: the spawn-form model and spawnSimilar into
components/spawn, the transcript's markdown/format helpers and the diff
into components/structured, the help overlay's grouping into
components/dialogs. Document-level event names now live in uiEvents.ts.

Deduplicated two pairs the migration left side by side: the sidebar
uses dialogs/KillDialog and common/ContextMenu. It also listens for the
command bar's kill/rename events, which nothing had picked up since
catalog.ts went away.

styles.css stays as the token and base layer, with `#app` renamed to
`#root` and the pane-body rules re-keyed off the classes the React
panes actually carry.

Closes #253

web/src/components/dialogs/HelpOverlay.test.tsx

@@ -3,7 +3,7 @@ import { cleanup, fireEvent, render, screen } from "@testing-library/react";
 import { afterEach, describe, expect, it } from "vitest";
 
 import { keyCaps } from "../../commands.js";
-import { groupedCommands } from "../../help.js";
+import { groupedCommands } from "./model.js";
 import { HelpOverlay } from "./HelpOverlay.js";
 
 afterEach(() => {

web/src/components/dialogs/HelpOverlay.tsx

@@ -6,7 +6,7 @@ import { useEffect, useState } from "react";
 import { createPortal } from "react-dom";
 
 import { CommandSet, defineCommands, keyCaps } from "../../commands.js";
-import { groupedCommands } from "../../help.js";
+import { groupedCommands } from "./model.js";
 
 export function HelpOverlay() {
   const [open, setOpen] = useState(false);

web/src/components/dialogs/index.ts

@@ -1,2 +1,3 @@
 export { KillDialog, type KillDialogProps } from "./KillDialog.js";
 export { HelpOverlay } from "./HelpOverlay.js";
+export { groupedCommands } from "./model.js";

web/src/components/dialogs/model.ts

@@ -0,0 +1,20 @@
+// Command-registry grouping for the help overlay. Moved out of help.ts (whose
+// imperative DOM overlay #253 deleted) so HelpOverlay.tsx renders the same
+// grouping the vanilla overlay did.
+
+import { publishedCommands, type Command } from "../../commands.js";
+
+/** Published commands bucketed by `group`, in registry order — the order the
+ *  overlay lists them in. */
+export function groupedCommands(): { title: string; items: Command[] }[] {
+  const groups: { title: string; items: Command[] }[] = [];
+  for (const cmd of publishedCommands()) {
+    let group = groups.find((g) => g.title === cmd.group);
+    if (!group) {
+      group = { title: cmd.group, items: [] };
+      groups.push(group);
+    }
+    group.items.push(cmd);
+  }
+  return groups;
+}