feat: webhook notification channel with UI and ingest dispatch

Add webhook config (DB/env), JSON POST on events/problems, settings API,
Settings UI section, and notify_dispatch for multi-channel ingest.

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/tests/test_settings_api.py

@@ -22,6 +22,56 @@ def test_get_notification_settings_masks_secrets(jwt_headers, client, monkeypatc
     assert body["telegram"]["min_severity"] == "warning"
     assert body["telegram"]["source"] == "env"
     assert body["telegram"]["bot_token_hint"].endswith("ghij")
+    assert "webhook" in body
+    assert body["webhook"]["enabled"] is False
+
+
+def test_put_webhook_settings_persists_db(jwt_headers, client, db_session, monkeypatch):
+    monkeypatch.setenv("WEBHOOK_ENABLED", "false")
+    monkeypatch.setenv("WEBHOOK_URL", "")
+    get_settings.cache_clear()
+
+    response = client.put(
+        "/api/v1/settings/notifications/webhook",
+        headers=jwt_headers,
+        json={
+            "enabled": True,
+            "min_severity": "warning",
+            "url": "https://example.com/hooks/sac",
+            "secret_header": "X-SAC-Token",
+            "secret": "supersecret",
+        },
+    )
+    assert response.status_code == 200
+    body = response.json()
+    assert body["source"] == "db"
+    assert body["configured"] is True
+
+    row = db_session.get(NotificationChannel, "webhook")
+    assert row is not None
+    assert row.webhook_url == "https://example.com/hooks/sac"
+    assert row.webhook_secret_header == "X-SAC-Token"
+
+
+def test_post_webhook_test_success(jwt_headers, client, db_session, monkeypatch):
+    monkeypatch.setenv("WEBHOOK_ENABLED", "false")
+    get_settings.cache_clear()
+
+    db_session.add(
+        NotificationChannel(
+            channel="webhook",
+            enabled=True,
+            min_severity="warning",
+            webhook_url="https://example.com/hook",
+        )
+    )
+    db_session.commit()
+
+    with patch("app.api.v1.settings.send_webhook_test_message") as mock_test:
+        response = client.post("/api/v1/settings/notifications/webhook/test", headers=jwt_headers)
+    assert response.status_code == 200
+    assert response.json()["ok"] is True
+    mock_test.assert_called_once()
 
 
 def test_put_telegram_settings_persists_db(jwt_headers, client, db_session, monkeypatch):