fix: address five review findings (NM retry loop, start_display message, code quality)

- wifi_monitor_daemon: reset _consecutive_internet_failures = 0 in both
  NM-restart exception handlers; previously both left the counter at threshold,
  causing an immediate retry on the next iteration instead of waiting another
  full backoff period

- api_v3: fix start_display failure message — when mode is set and systemctl
  returns non-zero, message now includes the failure reason and a hint rather
  than always reporting success phrasing

- wifi_manager: move _redirect_backend from class variable to instance variable
  in __init__ alongside _ap_enabled_at; class-level default shadowed correctly
  in practice (single instance) but was misleading

- wifi_manager: narrow broad except Exception in _check_internet_connectivity
  to (subprocess.SubprocessError, OSError) for ping and OSError for HTTP
  (urllib.error.URLError is an OSError subclass in Python 3)

- wifi_manager: remove redundant local 'import re as _re' in _validate_ap_config;
  re is already imported at module level (line 37)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

scripts/utils/wifi_monitor_daemon.py

@@ -153,10 +153,12 @@ class WiFiMonitorDaemon:
                                 self.wifi_manager._disconnected_checks = 0
                             except subprocess.CalledProcessError as e:
                                 logger.error(f"NetworkManager restart failed (rc={e.returncode}); "
-                                             "keeping failure counter unchanged")
+                                             "resetting failure counter to avoid tight retry loop")
+                                self._consecutive_internet_failures = 0
                             except Exception as e:
                                 logger.error(f"NetworkManager restart error: {e}; "
-                                             "keeping failure counter unchanged")
+                                             "resetting failure counter to avoid tight retry loop")
+                                self._consecutive_internet_failures = 0
                     else:
                         self._consecutive_internet_failures = 0
                 else: