feat: restart on SIGHUP in hbc and hbc_mini

Sets dorestart and triggers a clean shutdown; os.execv re-execs
the process with the original arguments after cleanup.

Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>

hbd/client/main.py

@@ -524,6 +524,13 @@ async def async_main(args, config):
     loop = asyncio.get_event_loop()
     for sig in (signal.SIGTERM, signal.SIGINT):
         loop.add_signal_handler(sig, stop)
+
+    def _sighup():
+        global dorestart
+        dorestart = True
+        stop()
+
+    loop.add_signal_handler(signal.SIGHUP, _sighup)
     
     # Start async tasks
     # Heartbeat senders (one per connection)