fix: recover from a PC/SC service failure without a server restart (v3.1.2)

After pcscd restarted (or the reader re-enumerated) the server stayed
permanently cardless:
- pyscard's presence-monitor thread stops itself on SCARD_E_NO_SERVICE
  and pyscard never starts it again, so card insertions were no longer
  noticed and auto-equip was dead;
- PCSCCardConnection.connect() reuses the context handle captured when
  the reader was opened, so the old connection could not be revived and
  every APDU kept failing with 'Service not available'.

- _start_card_watchdog(): a daemon that every 5 s checks whether
  CardMonitor().rmthread.instance is alive and recreates the stopped
  thread (CardMonitoringThread.instance = None + a fresh rmthread); the
  new thread reports already-present cards as inserted, which triggers
  auto-equip.  start_card_monitor() starts the watchdog.
- _is_pcsc_error(): pyscard exceptions carry an hresult, card-level
  errors do not; the disconnect paths (AUTO-STATUS, status poll, timer
  expiration, net-sim, tree, event send, OTA send) pass the verdict to
  _handle_card_disconnect(stale=...), which marks the transport stale.
- _ensure_transport(): builds a fresh transport via
  server.transport_factory (installed by __main__ as
  mod.init_reader(opts, **tracer_kwargs)) and installs it into
  app.sl/server.sl; called by the auto-equip worker, the /api/command
  equip branch and _esim_reinit.
- tests: watchdog tick, transport recreation (fresh/stale/failure/no
  factory), PC/SC classification, stale disconnect flag.
- docs: AGENTS card-behavior section, README troubleshooting (EN/RU);
  version 3.1.2, sw.js simple-v237.

README.md

@@ -700,6 +700,7 @@ pysim-simple-server --http-port 8080
 
 - **"Failed to establish context: Access denied"** — `pcscd` isn't running or the user lacks permission: `sudo systemctl enable --now pcscd && sudo usermod -a -G pcscd $USER`.
 - **"device file /dev/ttyUSB0 does not exist"** — no serial reader; connect a USB reader or pass `-d` explicitly. The server still starts without a reader.
+- **"Service not available" (0x8010001D) / reader gone after a `pcscd` restart** — the server recovers by itself: a watchdog revives pyscard's presence monitor and the next equip (automatic after re-insertion, or the **Equip** button) recreates the PC/SC transport. No server restart needed.
 
 ### API reference