feat: persist collapsible dashboard panels

tests/test_panel_persistence.py

@@ -0,0 +1,22 @@
+from pathlib import Path
+
+
+DASHBOARD = Path("frontend/index.html")
+
+
+def test_dashboard_panels_are_independently_collapsible():
+    html = DASHBOARD.read_text()
+
+    for panel_key in ("context", "ai-stream", "issues", "pull-requests", "widgets", "layout", "markdown"):
+        assert f'<details class="panel' in html
+        assert f'data-panel-key="{panel_key}"' in html
+
+
+def test_panel_open_state_is_restored_and_saved_in_local_storage():
+    html = DASHBOARD.read_text()
+
+    assert 'const PANEL_STATE_KEY = "stackchain.panel-state.v1"' in html
+    assert "localStorage.getItem(PANEL_STATE_KEY)" in html
+    assert "panel.open = savedState[panel.dataset.panelKey]" in html
+    assert "localStorage.setItem(PANEL_STATE_KEY" in html
+    assert "panel.addEventListener('toggle'" in html