test: improve coverage across frontend and backend

Frontend (22 → 37 tests):
- canvasStore: add tests for onNodesChange, onEdgesChange, onConnect,
  addNode with parentId, updateEdge, deleteEdge, setProxmoxContainerMode
  ON/OFF, loadCanvas parent-before-child ordering
- edgeColors: 6 tests for EDGE_DEFAULT_COLORS (all types, hex format, values)

Backend (40 → 80 tests):
- test_canvas (new): load empty canvas, default viewport, save creates/updates/
  deletes nodes+edges, viewport upsert, custom_colors, edge custom_color+path_style,
  auth guard
- test_fingerprint (new): match_port (known, unknown, wrong protocol, banner match,
  banner no-match, no banner), fingerprint_ports (matched, unknown, mixed, empty,
  default protocol), suggest_node_type (proxmox, server, generic, priority)
- test_nodes: update/delete 404, custom_colors CRUD, container_mode CRUD, auth guard
- test_edges: update edge, update/delete 404, custom_color, path_style, auth guard

backend/tests/test_edges.py

@@ -52,3 +52,51 @@ async def test_delete_edge(client: AsyncClient, headers: dict, two_nodes):
     res = await client.delete(f"/api/v1/edges/{edge_id}", headers=headers)
     assert res.status_code == 204
     assert len((await client.get("/api/v1/edges", headers=headers)).json()) == 0
+
+
+async def test_delete_edge_not_found(client: AsyncClient, headers: dict):
+    res = await client.delete("/api/v1/edges/nonexistent", headers=headers)
+    assert res.status_code == 404
+
+
+async def test_update_edge(client: AsyncClient, headers: dict, two_nodes):
+    src, tgt = two_nodes
+    edge_id = (await client.post("/api/v1/edges", json={"source": src, "target": tgt, "type": "ethernet"}, headers=headers)).json()["id"]
+    res = await client.patch(f"/api/v1/edges/{edge_id}", json={"type": "wifi", "label": "uplink"}, headers=headers)
+    assert res.status_code == 200
+    assert res.json()["type"] == "wifi"
+    assert res.json()["label"] == "uplink"
+
+
+async def test_update_edge_not_found(client: AsyncClient, headers: dict):
+    res = await client.patch("/api/v1/edges/nonexistent", json={"type": "wifi"}, headers=headers)
+    assert res.status_code == 404
+
+
+async def test_create_edge_with_custom_color(client: AsyncClient, headers: dict, two_nodes):
+    src, tgt = two_nodes
+    res = await client.post("/api/v1/edges", json={"source": src, "target": tgt, "type": "ethernet", "custom_color": "#a855f7"}, headers=headers)
+    assert res.status_code == 201
+    assert res.json()["custom_color"] == "#a855f7"
+
+
+async def test_create_edge_with_path_style(client: AsyncClient, headers: dict, two_nodes):
+    src, tgt = two_nodes
+    res = await client.post("/api/v1/edges", json={"source": src, "target": tgt, "type": "ethernet", "path_style": "smooth"}, headers=headers)
+    assert res.status_code == 201
+    assert res.json()["path_style"] == "smooth"
+
+
+async def test_update_edge_custom_color_and_path_style(client: AsyncClient, headers: dict, two_nodes):
+    src, tgt = two_nodes
+    edge_id = (await client.post("/api/v1/edges", json={"source": src, "target": tgt, "type": "ethernet"}, headers=headers)).json()["id"]
+    res = await client.patch(f"/api/v1/edges/{edge_id}", json={"custom_color": "#39d353", "path_style": "smooth"}, headers=headers)
+    assert res.status_code == 200
+    assert res.json()["custom_color"] == "#39d353"
+    assert res.json()["path_style"] == "smooth"
+
+
+async def test_create_edge_requires_auth(client: AsyncClient, two_nodes):
+    src, tgt = two_nodes
+    res = await client.post("/api/v1/edges", json={"source": src, "target": tgt, "type": "ethernet"})
+    assert res.status_code == 403