refactor(web): remove --dev; mount the reload chain unconditionally

The client-hmr row joins the web bundle as an ordinary always-on roster
row: without a rebuild watcher rewriting client bundles it polls
unchanged files and stays idle. This deletes the --dev flag, the web
runtime's mode config, the mode-forked prompt contract, the DSH_WEB_MODE
bash variable, and the post-settlement row-creation machinery the
conditional row required. dsh web + pnpm run dev:web remains the
development loop.

packages/client/hmr/src/index.ts

@@ -4,7 +4,9 @@
  * mounts deliver no inotify events), reports content changes through
  * `clientModuleHost.rebuilt(id)`, and serves the `/plugins/events` SSE channel
  * broadcasting graph/rebuilt frames to the browser half (src/client/).
- * Dev-only row: prod compositions never mount this plugin.
+ * The web bundle mounts this row unconditionally: without a rebuild
+ * watcher rewriting client bundles, the poll observes no changes and the
+ * chain stays idle.
  */
 import { statSync } from 'node:fs'
 import type { ServerResponse } from 'node:http'