fix: settings thresholds show correct per-config metrics; misc hbc fixes

Settings page: pass threshold_checker to http.start so the Threshold
Configurations section has data. Use threshold_checker's already-parsed
ThresholdConfig objects instead of re-parsing the raw nested YAML.
Named (non-default) configs now display only their explicit overrides
via threshold_raw_configs, not the full merged set with defaults.

hbc/hbc_mini: send boot and shutdown messages on first connection only
to avoid duplicate packets when multiple servers are configured.
Replace print("Daemonizing...") with logging.info so output goes to
syslog in daemon mode.

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

hbd/server/http.py

@@ -890,7 +890,7 @@ async def start(
         tmpl = env.get_template("settings.html")
         body = tmpl.render(
             title="Settings - Heartbeat",
-            sections=settings_mod.get_settings_sections(config),
+            sections=settings_mod.get_settings_sections(config, threshold_checker=threshold_checker),
             current_user=current_user.to_dict() if current_user else None,
             active_page="settings",
         )