test: add e2e coverage for image crop, curve widget, minimap, mask editor, painter

New specs:
- imageCrop.spec.ts: 6 tests (empty state, bounding box, ratio selector, lock toggle, presets, programmatic update)
- curveWidget.spec.ts: 6 tests (render, add/remove/drag points, interpolation mode, min-points guard)

Deepened existing specs:
- minimap.spec.ts: +6 tests (click-to-pan, drag-to-pan, zoom viewport, node changes, workflow reload, pan state)
- maskEditor.spec.ts: +10 tests (brush drawing, undo/redo, clear, cancel, invert, keyboard undo, tools, settings, save, eraser)
- painter.spec.ts: +11 tests (clear, eraser, control visibility, brush size, stroke widths, canvas controls, background, multi-stroke, color picker, opacity, partial erase)

browser_tests/assets/widgets/curve_widget.json

@@ -0,0 +1,56 @@
+{
+  "last_node_id": 1,
+  "last_link_id": 0,
+  "nodes": [
+    {
+      "id": 1,
+      "type": "CurveEditor",
+      "pos": [50, 50],
+      "size": [400, 500],
+      "flags": {},
+      "order": 0,
+      "mode": 0,
+      "inputs": [
+        {
+          "name": "curve",
+          "type": "CURVE",
+          "link": null
+        },
+        {
+          "name": "histogram",
+          "type": "HISTOGRAM",
+          "link": null
+        }
+      ],
+      "outputs": [
+        {
+          "name": "curve",
+          "type": "CURVE",
+          "links": null
+        }
+      ],
+      "properties": {
+        "Node name for S&R": "CurveEditor"
+      },
+      "widgets_values": [
+        {
+          "points": [
+            [0, 0],
+            [1, 1]
+          ],
+          "interpolation": "monotone_cubic"
+        }
+      ]
+    }
+  ],
+  "links": [],
+  "groups": [],
+  "config": {},
+  "extra": {
+    "ds": {
+      "offset": [0, 0],
+      "scale": 1
+    }
+  },
+  "version": 0.4
+}