fix(desktop): recover chat after sleep/wake by revalidating a stale remote backend

After sleep/wake, a remote (global-remote) primary backend can become
unreachable, but it has no child process whose 'exit' clears the main
process's cached connectionPromise. The renderer then re-dials the same
dead remote forever and the composer stays stuck on "Starting Hermes…";
only a quit+reopen recovered.

Fix: the renderer's existing backoff-paced reconnect loop now asks the
main process to revalidate the cached connection before re-dialing. The
main process liveness-probes the cached REMOTE backend's public
/api/status and, if unreachable, drops the cache (resetHermesConnection
only nulls connectionPromise for a remote — no child to SIGTERM) so the
next getConnection() rebuilds a reachable descriptor. Local backends are
never touched here; they self-heal via the child 'exit' handler. The
renderer's loop already provides retry pacing and rides out transient
blips, so no streak/episode bookkeeping is needed in the main process.

The boot hook dismisses the boot-progress overlay on the post-rebuild
'open' so an in-place rebuild can't leave it stuck at ~94%.

Reimplements #40135 by @AlchemistChaos on a smaller, more interpretable
path (63 added lines vs 555): no extracted helper module, no
failure-streak / episode-window state, the renderer's backoff loop is
the retry mechanism. Original diagnosis and fix by @AlchemistChaos.

Co-authored-by: AlchemistChaos <alchemistchaos@protonmail.com>

apps/desktop/electron/preload.cjs

@@ -2,6 +2,7 @@ const { contextBridge, ipcRenderer, webUtils } = require('electron')
 
 contextBridge.exposeInMainWorld('hermesDesktop', {
   getConnection: profile => ipcRenderer.invoke('hermes:connection', profile),
+  revalidateConnection: () => ipcRenderer.invoke('hermes:connection:revalidate'),
   touchBackend: profile => ipcRenderer.invoke('hermes:backend:touch', profile),
   getGatewayWsUrl: profile => ipcRenderer.invoke('hermes:gateway:ws-url', profile),
   getBootProgress: () => ipcRenderer.invoke('hermes:boot-progress:get'),