hub: restore-test "passed with warnings" visibility (v0.7.5)

Phase B (hub half) of the restore-test warning fix. The agent v0.7.0 now passes a
restore-test that emitted a benign start advisory (systemd-nesting) and carries the
warning text on the wire.

- hostRestoreTest gains warnings + warnings_recognized mirror fields (omitempty;
  absent recognized => false => louder unrecognized path)
- ingest logs [INFO] passed WITH WARNINGS (recognized), [WARN] for unrecognized;
  FAILED still [WARN]
- golden restore_tests[0] gains the keys, byte-identical with felhom-agent (sha256
  e6999d77...); bidirectional key-set contract test round-trips them
- no dashboard widget: no host-domain dashboard surface exists yet (log+persist only,
  as with pbs_snapshots) -- deferred to slice 10

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

hub/internal/api/testdata/host-report.golden.json

@@ -108,7 +108,11 @@
       "pass": true,
       "verified": "boot+running",
       "tested_at": "2026-06-09T11:05:00Z",
-      "duration_seconds": 38.2
+      "duration_seconds": 38.2,
+      "warnings": [
+        "WARN: Systemd 257 detected. You may need to enable nesting."
+      ],
+      "warnings_recognized": true
     }
   ],
   "pbs_snapshots": [