feat: replace static hardware fields with dynamic node properties

Replaces the 4 fixed hardware columns (cpu_count, cpu_model, ram_gb,
disk_gb) with a flexible properties system. Each property has a key,
value, icon (from a curated Lucide picker), and a visibility toggle
that controls whether it appears on the canvas node card.

- Backend: add `properties` JSON column to Node model; data migration
  converts existing hardware rows to properties with correct icons
  (idempotent, old columns kept for safety)
- Backend: add `properties` to NodeBase, NodeUpdate, NodeSave schemas
  and canvasSerializer so values survive canvas save/load
- Frontend: add NodeProperty type; new propertyIcons.ts registry (20
  icons); BaseNode renders visible properties with legacy hardware
  fallback for unmigrated nodes
- Frontend: DetailPanel gains interactive properties section (add /
  edit / remove / toggle visibility / icon picker) replacing the
  read-only hardware block; hardware section removed from NodeModal
- Tests: 6 migration tests, 7 API tests, 8 DetailPanel property tests,
  6 BaseNode render/fallback tests, 9 propertyIcons util tests

backend/tests/test_nodes.py

@@ -115,3 +115,97 @@ async def test_update_node_parent_id(client: AsyncClient, headers: dict):
 async def test_create_node_requires_auth(client: AsyncClient):
     res = await client.post("/api/v1/nodes", json={"type": "server", "label": "N", "status": "unknown"})
     assert res.status_code == 401
+
+
+# --- Properties tests ---
+
+async def test_create_node_default_properties_empty(client: AsyncClient, headers: dict):
+    """New node has an empty properties list by default."""
+    res = await client.post("/api/v1/nodes", json={"type": "server", "label": "Srv", "status": "unknown"}, headers=headers)
+    assert res.status_code == 201
+    assert res.json()["properties"] == []
+
+
+async def test_create_node_with_properties(client: AsyncClient, headers: dict):
+    """Node created with properties round-trips correctly."""
+    props = [
+        {"key": "CPU Model", "value": "i7-12700K", "icon": "Cpu", "visible": True},
+        {"key": "RAM", "value": "32 GB", "icon": "MemoryStick", "visible": False},
+    ]
+    res = await client.post(
+        "/api/v1/nodes",
+        json={"type": "server", "label": "Srv", "status": "unknown", "properties": props},
+        headers=headers,
+    )
+    assert res.status_code == 201
+    assert res.json()["properties"] == props
+
+
+async def test_patch_node_properties(client: AsyncClient, headers: dict):
+    """PATCH with properties replaces the full properties array."""
+    create = await client.post("/api/v1/nodes", json={"type": "server", "label": "Srv", "status": "unknown"}, headers=headers)
+    node_id = create.json()["id"]
+
+    props = [{"key": "Disk", "value": "2 TB", "icon": "HardDrive", "visible": True}]
+    res = await client.patch(f"/api/v1/nodes/{node_id}", json={"properties": props}, headers=headers)
+    assert res.status_code == 200
+    assert res.json()["properties"] == props
+
+
+async def test_patch_node_without_properties_does_not_wipe(client: AsyncClient, headers: dict):
+    """PATCH that omits properties leaves existing properties untouched."""
+    props = [{"key": "GPU", "value": "RTX 4090", "icon": "Monitor", "visible": True}]
+    create = await client.post(
+        "/api/v1/nodes",
+        json={"type": "server", "label": "Srv", "status": "unknown", "properties": props},
+        headers=headers,
+    )
+    node_id = create.json()["id"]
+
+    # PATCH only the label — properties must survive
+    res = await client.patch(f"/api/v1/nodes/{node_id}", json={"label": "Updated"}, headers=headers)
+    assert res.status_code == 200
+    assert res.json()["properties"] == props
+    assert res.json()["label"] == "Updated"
+
+
+async def test_patch_node_clears_properties_with_empty_array(client: AsyncClient, headers: dict):
+    """PATCH with properties=[] explicitly clears all properties."""
+    props = [{"key": "CPU Model", "value": "i5", "icon": "Cpu", "visible": True}]
+    create = await client.post(
+        "/api/v1/nodes",
+        json={"type": "server", "label": "Srv", "status": "unknown", "properties": props},
+        headers=headers,
+    )
+    node_id = create.json()["id"]
+
+    res = await client.patch(f"/api/v1/nodes/{node_id}", json={"properties": []}, headers=headers)
+    assert res.status_code == 200
+    assert res.json()["properties"] == []
+
+
+async def test_get_node_returns_properties(client: AsyncClient, headers: dict):
+    """GET /nodes/:id returns the properties field."""
+    props = [{"key": "OS", "value": "Debian 12", "icon": "Server", "visible": True}]
+    create = await client.post(
+        "/api/v1/nodes",
+        json={"type": "server", "label": "Srv", "status": "unknown", "properties": props},
+        headers=headers,
+    )
+    node_id = create.json()["id"]
+
+    res = await client.get(f"/api/v1/nodes/{node_id}", headers=headers)
+    assert res.status_code == 200
+    assert res.json()["properties"] == props
+
+
+async def test_properties_icon_can_be_null(client: AsyncClient, headers: dict):
+    """A property with icon=null is valid and round-trips correctly."""
+    props = [{"key": "Notes", "value": "custom value", "icon": None, "visible": False}]
+    create = await client.post(
+        "/api/v1/nodes",
+        json={"type": "generic", "label": "G", "status": "unknown", "properties": props},
+        headers=headers,
+    )
+    assert create.status_code == 201
+    assert create.json()["properties"] == props