feat(web): grow real node halves in connection and hmr

connection binds the web transport: it injects httpServer + apiProxy and
registers toFetchHandler(ctx.apiProxy) under the /api prefix (the node:http
to fetch bridge moves in from the webserver, keeping the res-close disconnect
detection and drain/close backpressure waits). hmr owns dev reload: a
stat-poll watch per graph row driven by clientModuleHost.onGraphChanged,
rebuilt(id) on content change, and the /plugins/events SSE route (GET/HEAD
guarded); frame types are single-sourced in events.ts shared by both halves.

packages/client/hmr/src/events.ts

@@ -0,0 +1,16 @@
+/**
+ * Wire protocol of the `/plugins/events` dev SSE channel — single source for
+ * both halves of this package. Frames still cross a wire boundary: the
+ * browser half validates them at its JSON parse point; sharing the type keeps
+ * the two ends from drifting, not from parsing.
+ */
+
+import type { WebBootGraph } from '@deepseek-ai/dsh-client-modules'
+
+/** One SSE frame: the full graph on connect, or one rebuilt bundle notice. */
+export type PluginsEventFrame =
+  | { type: 'graph'; graph: WebBootGraph }
+  | { type: 'rebuilt'; id: string; rev: string }
+
+/** System SSE endpoint pushing graph/rebuilt frames (wire protocol constant). */
+export const EVENTS_ENDPOINT = '/plugins/events'