feat: replace YAML hosts editor with form-based CRUD table

Settings > Hosts now renders a table with per-column controls
(watch, dyndns, owner, managers/monitors multi-select, threshold
config, notification channels) instead of a raw YAML textarea.
Changes stage via the existing Publish flow like other form sections.

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

hbd/server/settings.py

@@ -436,7 +436,7 @@ def get_settings_sections(config: dict, threshold_checker=None) -> list:
             "id": "hosts",
             "title": "Hosts",
             "description": "Host definitions loaded from the config file.",
-            "section_mode": "yaml",
+            "section_mode": "hosts",
             "api_section": "hosts",
             "hosts": hosts_list,
             "fields": [],
@@ -475,4 +475,16 @@ def get_settings_data(config: dict, threshold_checker=None) -> dict:
     """Return sections list + auxiliary data for the settings template."""
     sections = get_settings_sections(config, threshold_checker=threshold_checker)
     all_channel_names = sorted((config.get("notification_channels") or {}).keys())
-    return {"sections": sections, "all_channel_names": all_channel_names}
+    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 []
+    )
+    return {
+        "sections": sections,
+        "all_channel_names": all_channel_names,
+        "all_usernames": all_usernames,
+        "all_threshold_configs": all_threshold_configs,
+    }