feat: add _build_host_info helper for host info endpoint

Extracts host info assembly (owner, managers, hbc version/type,
last packet timestamp, threshold configs) into a testable module-level
helper, with 10 covering tests.

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

hbd/server/http.py

@@ -126,6 +126,46 @@ def _mask_config_for_api(config) -> dict:
     return result
 
 
+def _build_host_info(host, threshold_checker=None) -> dict:
+    """Assemble the info payload for GET /api/0/hosts/{hostname}/info."""
+    hbc_version = None
+    hbc_type = None
+    latest_os = host.get_latest_plugin_data("os_info")
+    if latest_os:
+        _, os_data = latest_os
+        hbc_version = os_data.get("hbc_version")
+        hbc_type = os_data.get("hbc_type")
+
+    last_packet = None
+    if host.connections:
+        last_packet = max(conn.lastbeat for conn in host.connections.values())
+
+    thresholds = None
+    if threshold_checker is not None:
+        raw = threshold_checker.get_thresholds_for_host(host.name)
+        thresholds = sorted(
+            [
+                {
+                    "metric": tc.metric_path,
+                    "warning": tc.warning,
+                    "critical": tc.critical,
+                    "operator": tc.operator.value,
+                }
+                for tc in raw.values()
+            ],
+            key=lambda x: x["metric"],
+        )
+
+    return {
+        "owner": getattr(host, "owner", None),
+        "managers": list(getattr(host, "managers", [])),
+        "hbc_version": hbc_version,
+        "hbc_type": hbc_type,
+        "last_packet": last_packet,
+        "thresholds": thresholds,
+    }
+
+
 async def start(
     host: str,
     port: int,