Session-recovery robustness (from PR #1)

- Suppress ConnectionError log noise from in-flight requests draining
  after a session close (poll_scheduler + keepalive log at DEBUG).
- Null KeepaliveTask.on_unreachable during a forced reconnect so the
  dying session's keepalive can't flip HA availability offline after
  the new session is already healthy. Ported into PR #5's
  _maybe_force_reconnect flow.

Drops the _session_stop / publish-health force-close mechanism from
the original PR — PR #5's last_success_ts + _maybe_force_reconnect
already covers the 'session dead, restart it' goal via a different
path, and running both means two paths force-closing the same session
on the same failure.

samsung_appliance/poll_scheduler.py

@@ -237,6 +237,11 @@ class PollScheduler:
                     self.log.warning("poll %s timeout (cooldown %.0fs)",
                                      href, cooldown)
                 return
+            except ConnectionError as e:
+                self._poll_error_count += 1
+                self._record_rtt((time.monotonic() - t0) * 1000.0)
+                if self.log: self.log.debug("poll %s: %s", href, e)
+                return
             except Exception as e:
                 self._poll_error_count += 1
                 self._record_rtt((time.monotonic() - t0) * 1000.0)
@@ -274,6 +279,11 @@ class PollScheduler:
                 self.log.warning("sweep %s timeout (cooldown %.0fs)",
                                  path, cooldown)
             return
+        except ConnectionError as e:
+            self._poll_error_count += 1
+            self._record_rtt((time.monotonic() - t0) * 1000.0)
+            if self.log: self.log.debug("sweep %s: %s", path, e)
+            return
         except Exception as e:
             self._poll_error_count += 1
             self._record_rtt((time.monotonic() - t0) * 1000.0)
@@ -300,4 +310,4 @@ class PollScheduler:
         if self.log:
             elapsed_ms = (time.monotonic() - t0) * 1000.0
             self.log.info("sweep complete (%d links, %.0fms)",
-                          len(indexed), elapsed_ms)
+                          len(indexed), elapsed_ms)