refactor(gui): host graph from dshClient discovery; webserver self-watches bundles for HMR

The registry scans mounted Loader entries' dshClient declarations and
composes __DSH_BOOT__ {rev, entries} — inject edges and the immediately
mark come from manifests, never hand-copied; malformed fields fail loud
at load. The composing app owns one flat roster plus the --dev switch
(hmr row and bundle watching are dev-graph decisions).

The rebuild signal is the webserver's own observation: in dev mode the
registry stat-polls each scanned bundle (fs.watchFile; polling because
network mounts deliver no inotify), re-hashes on change, and broadcasts
a rebuilt frame on the /plugins/events SSE channel only when the rev
actually changed. Watch membership follows the table across rescans;
dispose drops all watches; a torn read self-heals on the next tick.
The POST /plugins/rebuilt endpoint is gone — builders and the host
share zero protocol. dsh web --dev logs the watched bundle list and
each rebuilt id with its rev transition.

packages/host/runtime/src/index.ts

@@ -11,4 +11,4 @@ export { createApiProxy } from './api-proxy.ts'
 export type { ApiProxyDefaults } from './api-proxy.ts'
 export { startHost } from './start.ts'
 export type { StartHostOptions, RunningHost } from './start.ts'
-export { mountWebPlugins, WEB_UI_PLUGINS } from './web-plugins.ts'
+export { mountWebPlugins } from './web-plugins.ts'