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/structured/TranscriptRow.tsx

@@ -7,7 +7,7 @@
 
 import { useEffect, useRef, type ReactNode } from "react";
 
-import { renderInlineMarkdown, renderMarkdown, formatElapsed } from "../../structuredRender.js";
+import { renderInlineMarkdown, renderMarkdown, formatElapsed } from "./render.js";
 import type {
   AcpContentBlock,
   AcpPermissionOption,
@@ -35,7 +35,7 @@ import { ToolIcon } from "./ToolIcon.js";
 // content rows: user / agent / thought
 // ---------------------------------------------------------------------------
 
-/** Model-authored markdown, sanitized by structuredRender.ts before it enters
+/** Model-authored markdown, sanitized by render.ts before it enters
  *  the DOM. Tables get their own scroller and links open out of the app. */
 function Prose({ html }: { html: string }) {
   const ref = useRef<HTMLDivElement | null>(null);