Test disk health rows

Every test pins a way the card could start showing a failing or unreadable drive as fine, which is the only failure mode that matters here: nobody investigates a disk that looks healthy.

Covers failure-first ordering, null predictfailure reading as unknown rather than OK, unknown outranking OK, both sources surviving for one drive, order independence, and malformed payloads. The ranking was mutation-checked: swapping the unknown and OK ranks fails the suite.

Also updates the panel count assertion, which correctly caught the new card.

tests/test_plugins/test_endpoints_plugin.py

@@ -69,7 +69,7 @@ def test_endpoints_asset_panels_are_computer_scoped():
     """Every asset panel targets computer assets only, with an endpoint."""
     plugin = EndpointsPlugin()
     panels = plugin.get_asset_panels()
-    assert len(panels) == 12
+    assert len(panels) == 13
     for panel in panels:
         assert panel['assettypes'] == ['computer']
         assert panel['endpoint'].startswith('/api/endpoints/')