fix(mesh): setup modal re-fires on EVERY plug — dismissals key on plug time

detected_device_info now carries plugged_at (the /dev node's creation
time; udev recreates it per plug). Dismissals store (path -> plugged_at),
so swapping sticks or a fast unplug/replug between status polls can no
longer be suppressed by an old 'Not Now' (v1 path-only dismissals are
abandoned wholesale).

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

core/archipelago/src/mesh/serial.rs

@@ -572,6 +572,12 @@ pub struct DetectedDeviceInfo {
     pub pid: Option<String>,
     pub product: Option<String>,
     pub manufacturer: Option<String>,
+    /// Unix epoch seconds of the /dev node's creation — udev recreates the
+    /// node on every plug, so this changes on each replug. The UI keys its
+    /// "Not Now" dismissals on (path, plugged_at): swapping a stick (or
+    /// unplug/replug faster than a status poll) invalidates old dismissals
+    /// and the setup modal fires again, per the hot-swap UX (2026-07-22).
+    pub plugged_at: Option<u64>,
 }
 
 /// Like `detect_serial_devices`, but with USB metadata per port.
@@ -579,12 +585,19 @@ pub async fn detect_serial_devices_info() -> Vec<DetectedDeviceInfo> {
     let mut out = Vec::new();
     for path in detect_serial_devices().await {
         let usb = usb_info_for_tty(&path).await;
+        let plugged_at = tokio::fs::metadata(&path)
+            .await
+            .ok()
+            .and_then(|m| m.modified().ok())
+            .and_then(|t| t.duration_since(std::time::UNIX_EPOCH).ok())
+            .map(|d| d.as_secs());
         out.push(DetectedDeviceInfo {
             path,
             vid: usb.0,
             pid: usb.1,
             product: usb.2,
             manufacturer: usb.3,
+            plugged_at,
         });
     }
     out