fix(mesh): stop probing one physical radio as two devices

/dev/mesh-radio is a udev symlink to a ttyUSB*/ttyACM* node that is also
in SERIAL_CANDIDATES, so one board was detected, probed and DTR/RTS-reset
twice per reconnect cycle (and shown twice in the UI):

- detect_serial_devices() dedupes candidates by canonical path, keeping
  the stable /dev/mesh-radio name
- auto-detect fallback skips the preferred path it just probed this cycle
  instead of immediately resetting the same board again
- probe_device's active-session guard compares canonical paths, so a
  probe via the alias can no longer open the tty the live session holds

Together with the 2s boot-settle and stable-session backoff gate, this
takes a plugged-in CP2102/ESP32 board from up to 9 reset events per
cycle at a permanent 5s retry floor down to one probe sequence per
backoff window — enough for the radio to actually finish booting.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

core/archipelago/src/mesh/mod.rs

@@ -1063,8 +1063,18 @@ impl MeshService {
     /// with the reconnect loop (whichever loses just retries).
     pub async fn probe_device(&self, path: &str) -> Result<listener::DeviceProbe> {
         let status = self.state.status.read().await;
-        if status.device_connected && status.device_path.as_deref() == Some(path) {
-            anyhow::bail!("{path} is the active mesh radio — already connected");
+        if status.device_connected {
+            if let Some(active) = status.device_path.as_deref() {
+                // Compare canonical paths: /dev/mesh-radio is a symlink to the
+                // ttyUSB*/ttyACM* node, and a probe through the alias would
+                // still open the very tty the live session is holding.
+                let canon = |p: &str| {
+                    std::fs::canonicalize(p).unwrap_or_else(|_| std::path::PathBuf::from(p))
+                };
+                if canon(active) == canon(path) {
+                    anyhow::bail!("{path} is the active mesh radio — already connected");
+                }
+            }
         }
         drop(status);
         listener::probe_device(path).await