joystick UI: handle SENT_HEARD/UNHEARD in buildChannelReplyPrefix

After Phase J, the joystick UI rewrites a sent channel message's
path_len from OUT_PATH_SENT (0xFE) to OUT_PATH_SENT_HEARD (0xFD) or
OUT_PATH_SENT_UNHEARD (0xFC) once the feedback window resolves.
buildChannelReplyPrefix only excluded OUT_PATH_SENT, so a reply to
one of the user's own messages (post-feedback) would treat it as
incoming and build a garbled "@[<random body>]" prefix.

Also cleans up an awkward `class ContentionTracker&` qualifier in
Mesh.h.

zephcore/include/mesh/Mesh.h

@@ -34,13 +34,14 @@ class Mesh : public Dispatcher {
 	void routeDirectRecvAcks(Packet *packet, uint32_t delay_millis);
 	DispatcherAction forwardMultipartDirect(Packet *pkt);
 
+protected:
+	ContentionTracker _contention;
 public:
 	/* Made public so the UI layer can query/extract per-packet dupe counts
 	 * for outbound-flood feedback (joystick channel-send "heard a repeat?"). */
-	class ContentionTracker& getContentionTracker() { return _contention; }
-	const class ContentionTracker& getContentionTracker() const { return _contention; }
+	ContentionTracker& getContentionTracker() { return _contention; }
+	const ContentionTracker& getContentionTracker() const { return _contention; }
 protected:
-	ContentionTracker _contention;
 #ifdef CONFIG_ZEPHCORE_APC
 	PowerController _power_ctrl;
 	PowerController& getPowerController() { return _power_ctrl; }