feat: ServerState data model with serialization

Add dataclasses for ServerState, LoadingInfo, and Metrics to represent
the server's runtime state. ServerState includes a to_dict() method for
serialization with timestamp.

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

tests/test_log_parser.py

@@ -45,3 +45,51 @@ def test_classify_router_proxy_line():
     kind, port, content = classify_line(line)
     assert kind == "router"
     assert port is None
+
+
+# ── ServerState data model ───────────────────────────────────────────────────
+
+from log_parser import ServerState, LoadingInfo, Metrics
+
+
+def test_server_state_defaults():
+    s = ServerState()
+    assert s.state == "offline"
+    assert s.model is None
+    assert s.loading is None
+    assert s.request_count == 0
+
+
+def test_server_state_to_dict_offline():
+    s = ServerState()
+    d = s.to_dict()
+    assert d["state"] == "offline"
+    assert d["model"] is None
+    assert d["loading"] is None
+    assert d["metrics"]["gen_speed"] is None
+    assert "timestamp" in d
+
+
+def test_server_state_to_dict_loading():
+    s = ServerState(
+        state="loading",
+        model="Qwen3",
+        loading=LoadingInfo(stages=["text_model", "mmproj_model"], current="text_model", progress=0.5),
+    )
+    d = s.to_dict()
+    assert d["state"] == "loading"
+    assert d["loading"]["current"] == "text_model"
+    assert d["loading"]["progress"] == 0.5
+
+
+def test_server_state_to_dict_generating():
+    s = ServerState(
+        state="generating",
+        model="Qwen3",
+        metrics=Metrics(gen_speed=72.2, n_decoded=218),
+        request_count=5,
+    )
+    d = s.to_dict()
+    assert d["metrics"]["gen_speed"] == 72.2
+    assert d["metrics"]["n_decoded"] == 218
+    assert d["request_count"] == 5