fix(us-020): silence BrokenPipeError in tracker _send_json; deterministic node IDs; HF model coverage

- Wrap wfile.write in _TrackerHandler._send_json with except BrokenPipeError
- Replace uuid4 node IDs with deterministic SHA-256 hash of endpoint+model+shards
  so nodes keep the same ID on re-registration after tracker restart
- /v1/models now lists HF-repo models (not just preset models)
- /v1/coverage/{model} now resolves HF repos, not just preset names
- /v1/route response includes node_id alongside endpoint
- startup.py exposes tracker_node_id on node object and prints it in dashboard

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

tests/test_node_startup.py

@@ -370,6 +370,11 @@ def test_real_model_startup_summary_shows_total_layers(tmp_path, monkeypatch, ca
         lambda: {"device": "cpu", "gpu_name": None, "vram_mb": 0},
     )
     monkeypatch.setattr(startup_mod, "TorchNodeServer", FakeTorchNodeServer)
+    monkeypatch.setattr(
+        startup_mod,
+        "_post_json",
+        lambda _url, _payload, timeout=10.0: {"node_id": "node-test-123"},
+    )
 
     node = run_startup(
         tracker_url="http://127.0.0.1:8080",
@@ -380,8 +385,10 @@ def test_real_model_startup_summary_shows_total_layers(tmp_path, monkeypatch, ca
     )
 
     assert node.backend.total_layers == 24
+    assert node.tracker_node_id == "node-test-123"
     output = capsys.readouterr().out
     assert "Shard:        layers 0–23; 24 of 24" in output
+    assert "Node ID:      node-test-123" in output
 
 
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