fix: derive hosts threshold config list from config file keys

Previously all_threshold_configs was built from the threshold_checker
object, which may not be populated at render time, leaving the select
empty. Read directly from config["threshold_configs"] instead.

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

hbd/server/settings.py

@@ -476,12 +476,7 @@ def get_settings_data(config: dict, threshold_checker=None) -> dict:
     sections = get_settings_sections(config, threshold_checker=threshold_checker)
     all_channel_names = sorted((config.get("notification_channels") or {}).keys())
     all_usernames = sorted((config.get("users") or {}).keys())
-    # Threshold config names come from the parsed section data already in sections.
-    tc_section = next((s for s in sections if s["id"] == "thresholds"), None)
-    all_threshold_configs = (
-        [tc["name"] for tc in tc_section["threshold_configs"]]
-        if tc_section else []
-    )
+    all_threshold_configs = sorted((config.get("threshold_configs") or {}).keys())
     return {
         "sections": sections,
         "all_channel_names": all_channel_names,