fix(wallet): wait for the old node to fully exit before restarting on switch

After the stop, the switch started the replacement dragonxd too early — while the
old (direct-connected, unowned) node was still doing a slow graceful shutdown
(~70s; its network threads block on peer TLS timeouts) and holding the DATADIR
LOCK. The replacement couldn't acquire the lock, failed repeatedly, and the
crash-wedge left it stuck "starting". Root cause: the readiness poll used
isRpcPortInUse(), which on Windows is a connect() probe that reads "free" the
moment the daemon stops ACCEPTING RPC — early in shutdown, long before the
process exits and releases the datadir.

- EmbeddedDaemon::isDaemonProcessRunning(): true while any dragonxd process is
  alive (Windows findProcessByName; Linux /proc/<pid>/comm scan; macOS port
  fallback) — reflects the PROCESS, not just RPC acceptance.
- stopDaemonForWalletSwitch: for an UNOWNED node (no handle), after the RPC stop
  wait until BOTH the port is free AND isDaemonProcessRunning() is false, bounded
  ~120s (or ~5s if the stop couldn't be sent). Owned nodes are unchanged
  (stopEmbeddedDaemon() blocks for exit via the handle).
- Switch notification reworded to set the up-to-a-minute expectation (60s toast).

daemon_restarting_ stays set across the wait so the connect loop can't spawn a
competing daemon. Adversarially verified 6/6; fixes the seed-adopt path too.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/daemon/embedded_daemon.h

@@ -221,6 +221,15 @@ public:
      */
     void setSkipPortCheck(bool v) { skip_port_check_ = v; }
 
+    /**
+     * @brief True while ANY dragonxd process is running (by process name), regardless of who started it.
+     *        Unlike isRpcPortInUse()/isRunning(), this reflects the actual PROCESS still being alive — a
+     *        graceful shutdown stops accepting RPC (port reads "free") but keeps the datadir lock until the
+     *        process exits, which can take up to ~90s. Use this to know a stopped node has FULLY released
+     *        the datadir before starting a replacement. Matches the daemon binary name on all platforms.
+     */
+    static bool isDaemonProcessRunning();
+
     /** @brief Is an arbitrary TCP port currently in use on localhost? (used to pick a free port) */
     static bool tcpPortInUse(int port);