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/configio.py

@@ -89,6 +89,8 @@ def apply_structured_section(data, section: str, values: dict) -> None:
                 data[key] = values[key]
     elif section == "users":
         data["users"] = values
+    elif section == "hosts":
+        data["hosts"] = values
     else:
         raise ValueError(f"Unknown structured section: {section!r}")