feat: страница логов /ui/logs с SSE real-time потоком

- log_buffer: RingBufferHandler, кольцевой буфер 600 записей, fan-out SSE
- ui_logs: GET /ui/logs (HTML), GET /ui/logs/stream (EventSource)
- main: install_log_handler при старте, подключён router логов
- nav_rail: ссылка Логи, root_html: кнопка-ссылка Логи
- Исправлено: NaN/Inf/NUL в теле вебхука → 500 от PostgreSQL jsonb
- Тесты: test_log_buffer, test_json_sanitize; 51 passed

Made-with: Cursor

tests/test_log_buffer.py

@@ -0,0 +1,45 @@
+"""Кольцевой буфер логов и SSE-страница."""
+
+import logging
+
+import pytest
+from fastapi.testclient import TestClient
+
+from onguard24 import log_buffer
+
+
+def test_ring_buffer_captures_log_records() -> None:
+    log_buffer._ring.clear()
+    handler = log_buffer.RingBufferHandler()
+    handler.setFormatter(logging.Formatter("%(name)s %(message)s"))
+    logger = logging.getLogger("test.ring")
+    logger.addHandler(handler)
+    logger.setLevel(logging.DEBUG)
+    try:
+        logger.info("hello ring")
+        history = log_buffer.get_history()
+        assert any("hello ring" in e["msg"] for e in history)
+    finally:
+        logger.removeHandler(handler)
+        log_buffer._ring.clear()
+
+
+def test_logs_page_returns_html(client: TestClient) -> None:
+    r = client.get("/ui/logs")
+    assert r.status_code == 200
+    assert "text/html" in r.headers.get("content-type", "")
+    assert "Логи" in r.text
+    assert "log-wrap" in r.text
+    assert "EventSource" in r.text or "event-stream" in r.text or "ui/logs/stream" in r.text
+
+
+def test_logs_page_in_nav_rail(client: TestClient) -> None:
+    r = client.get("/ui/logs")
+    assert r.status_code == 200
+    assert "/ui/logs" in r.text
+
+
+def test_root_has_logs_link(client: TestClient) -> None:
+    r = client.get("/")
+    assert r.status_code == 200
+    assert "/ui/logs" in r.text