feat(gui): dsh-client-hmr reload driver and the dshClient-discovered watch-build script

client-hmr is a normal plugin package composed into dev graphs only. It
listens on /plugins/events and reloads one plugin per rebuilt frame,
serialized: invalidate, prefetch (fresh factory registers while the old
fiber still serves), registry.delete before touching the fiber, drain
disposers, drop owned style tags, entry.refresh(), fiber.await() loud.
Dependency cascade costs zero client code — fiber activation epochs
re-load dependents through cordis itself. Reload is coarse by design;
no rollback in v1; self-reload works with a frame gap the next rebuild
heals.

scripts/dev-web.ts (pnpm run dev:web) is the convenience watch-build:
it discovers its package list by scanning packages/*/*/package.json for
dshClient platform "web" at startup — no hardcoded roster — and talks
no protocol to the host. Gate bookkeeping rides along: knip entries for
the new packages, README model-experience allowlist rows.

packages/client/hmr/tsdown.config.ts

@@ -0,0 +1,3 @@
+import { clientBundle } from '../tsdown.client.ts'
+
+export default clientBundle('@deepseek-ai/dsh-client-hmr', ['lib/types/index.js', 'lib/types/invariant.js'])