fix(reaction): Stamp connect times from the ACL broadcast

The connection timestamp cache was only maintained while the connected-devices
flow had a subscriber. If the process died while a device stayed connected and
that device then disconnected and reconnected with nothing running, the
restarted collection found the old entry still keyed by a currently-connected
address, kept it through the prune, and reported the original connect time —
so the popup age check rejected an arbitrarily old connection.

The ACL broadcasts arrive at a manifest-registered receiver that wakes the
process regardless of any flow subscription, so the stamp is taken there
instead: connect stamps (keeping an existing one, which is the earlier and
therefore truer time), disconnect drops the entry. The flow keeps its own
stamp-on-first-sight and prune as a backstop for the force-stopped state and
missed broadcasts.

ACL_DISCONNECTED was already in the receiver's expected actions but was never
registered in the manifest. It does not start the monitor: a disconnect is not
a reason to start monitoring, and the start triggers here are deliberately
conservative.

app/src/main/AndroidManifest.xml

@@ -86,6 +86,7 @@
             android:label="Service trigger">
             <intent-filter>
                 <action android:name="android.bluetooth.device.action.ACL_CONNECTED" />
+                <action android:name="android.bluetooth.device.action.ACL_DISCONNECTED" />
             </intent-filter>
         </receiver>