feat(R08): split ScheduleTaskTab, FolderTab, DashboardTab, StructureGraphView

Team Hoa, EPIC R08 (UI/Application Separation) - Team Hoa scope only
(R08-T11 -> T14; R08-T01->T10 belong to Team Duy/Team Nam).

- R08-T11: ui/schedule_task_tab.py (795 lines) -> presentation/scheduling/
  {kanban_board_widget,calendar_view_widget,ai_task_creator_dialog,
  ai_task_import_dialog,run_history_dialog}.py + schedule_task_tab.py
  shell. Kanban CRUD/drag-drop now goes through
  application/scheduling/task_application_service.py (R07-T04) instead of
  ~30 lines of inline if/elif per drag target.
- R08-T12: ui/folder_tab.py (1587 lines, the largest of the four) ->
  presentation/folder/{workspace_file_tree,document_preview_manager,
  code_editor,office_document_renderer,ai_file_editor_dialog,
  ai_edit_model_resolver,ai_edit_pipeline}.py + folder_tab.py shell.
  Closes the R06-T05 loop: FileWorkspaceService existed since R06 with
  zero production call sites (confirmed by grep); every plain-text write
  (save/create/write_content) now goes through it, gaining path
  containment and a Python-syntax warning the original code never had.
  Pure helpers (_read_text, _is_probably_text, _pptx_available,
  _split_code_block, _parse_ai_output) moved to
  application/workspaces/{file_preview_helpers,ai_edit_output}.py.
- R08-T13: ui/dashboard_tab.py (437 lines) -> presentation/dashboard/
  {token_usage_card_widget,usage_chart_widget,habits_widget}.py +
  dashboard_tab.py shell, backed by a new
  application/monitoring/dashboard_query_service.py (pricing/period/
  summary queries the three widgets used to each recompute separately).
  Directory-ownership note left in the checklist for Team Nam.
- R08-T14: ui/structure_graph_view.py (1035 lines) ->
  presentation/graph/{graph_scene_items,graph_renderer,
  graph_messages_view,graph_qa_widget}.py + structure_graph_view.py
  shell. Extraction helpers (_pdf_to_markdown, _extract_file_contents)
  moved to application/workspaces/graph_index_service.py (pure Python).
  Renderer and Q&A panel talk only through signals
  (node_selected/graph_rendered/raw_json_ready/project_changed) - neither
  imports the other.
- presentation/shared/web_engine_support.py: HAS_WEB_ENGINE, previously
  duplicated (folder_tab imported it FROM structure_graph_view.py) - now
  one shared flag instead of one screen importing another screen's module.

All four old ui/*.py files deleted; app.py and ui/workspace_tab.py updated
to the new import paths (each god-file only had 1-2 real construction
sites, so import sites were updated directly rather than kept as a
strangler-fig shim - unlike core/tools.py at R05, which had dozens).

pytest: 377 pass (+94 vs the R07 baseline of 328; same 4 pre-existing
failures as the R05/R06 baseline, unrelated to this work).
scripts/check_imports.py: PASS. python -c "import cowork_local.app": OK.
Every new file < 400 lines (largest: graph_renderer.py, 391).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tests/integration/test_structure_graph_view.py

@@ -0,0 +1,162 @@
+"""EPIC R08-T14: GraphRenderer / GraphQaWidget / StructureGraphView shell,
+real Qt offscreen.
+
+Scope note: a real directory SCAN (``GraphRenderer._scan``) runs on a
+``core.worker.AgentWorker`` QThread and had no existing test before this
+task either (grep confirms nothing under tests/ exercised
+``ui/structure_graph_view.py``). These tests drive ``_render()`` directly
+with a hand-built ``StructureGraph`` instead of a live scan — enough to
+prove the renderer <-> Q&A wiring (the actual R08-T14 deliverable) without
+needing a real codebase to walk.
+"""
+from __future__ import annotations
+
+import os
+
+import pytest
+
+os.environ.setdefault("QT_QPA_PLATFORM", "offscreen")
+
+from cowork_local.config import AppConfig  # noqa: E402
+from cowork_local.core.structure_graph import GEdge, GNode, StructureGraph  # noqa: E402
+from cowork_local.state import AppContext  # noqa: E402
+
+pytest.importorskip("PySide6", reason="Qt is required for the integration suite")
+
+
+@pytest.fixture(scope="module")
+def qt_app():
+    from PySide6.QtWidgets import QApplication
+
+    return QApplication.instance() or QApplication([])
+
+
+@pytest.fixture
+def ctx(qt_app, tmp_path):
+    return AppContext(AppConfig.load(tmp_path / "config.json"))
+
+
+def _fake_graph(tmp_path):
+    f = tmp_path / "mod.py"
+    f.write_text("def hello():\n    pass\n", encoding="utf-8")
+    nodes = [
+        GNode(id="n1", label="mod.py", kind="file", detail="a module", path=str(f)),
+        GNode(id="n2", label="hello", kind="function", detail="says hi", path=str(f)),
+    ]
+    edges = [GEdge(source="n1", target="n2", type="defines")]
+    return StructureGraph(nodes=nodes, edges=edges)
+
+
+def test_structure_graph_view_builds(ctx):
+    from cowork_local.presentation.graph.structure_graph_view import StructureGraphView
+
+    view = StructureGraphView(ctx)
+    assert view.renderer is not None
+    assert view.qa is not None
+
+
+def test_render_populates_the_scene_and_emits_graph_rendered(ctx, tmp_path):
+    from cowork_local.presentation.graph.graph_renderer import GraphRenderer
+
+    renderer = GraphRenderer(ctx)
+    graph = _fake_graph(tmp_path)
+    seen = []
+    renderer.graph_rendered.connect(lambda: seen.append(1))
+
+    renderer._render({"graph": graph, "pos": {"n1": (0, 0), "n2": (100, 0)}, "seq": renderer._scan_seq})
+
+    assert renderer.graph is graph
+    assert len(renderer._node_items) == 2
+    assert seen == [1]
+
+
+def test_render_ignores_a_stale_scan_result(ctx, tmp_path):
+    """Only the LATEST scan's result is ever rendered (no stale overwrite)."""
+    from cowork_local.presentation.graph.graph_renderer import GraphRenderer
+
+    renderer = GraphRenderer(ctx)
+    first = _fake_graph(tmp_path)
+    renderer._render({"graph": first, "pos": {}, "seq": renderer._scan_seq})
+    renderer._scan_seq += 1   # a second scan started
+
+    stale = StructureGraph(nodes=[], edges=[])
+    renderer._render({"graph": stale, "pos": {}, "seq": renderer._scan_seq - 1})
+
+    assert renderer.graph is first   # stale result was dropped
+
+
+def test_node_selection_updates_the_qa_detail_panel(ctx, tmp_path):
+    from cowork_local.presentation.graph.graph_qa_widget import GraphQaWidget
+    from cowork_local.presentation.graph.graph_renderer import GraphRenderer
+
+    renderer = GraphRenderer(ctx)
+    graph = _fake_graph(tmp_path)
+    renderer._render({"graph": graph, "pos": {"n1": (0, 0), "n2": (100, 0)}, "seq": renderer._scan_seq})
+    qa = GraphQaWidget(ctx, renderer)
+
+    node = graph.nodes[1]
+    renderer.node_selected.emit(node)
+
+    assert "hello" in qa.detail.toPlainText()
+    assert "says hi" in qa.detail.toPlainText()
+
+
+def test_candidate_file_paths_uses_selected_nodes_when_present(ctx, tmp_path):
+    from cowork_local.presentation.graph.graph_qa_widget import GraphQaWidget
+    from cowork_local.presentation.graph.graph_renderer import GraphRenderer
+
+    renderer = GraphRenderer(ctx)
+    graph = _fake_graph(tmp_path)
+    renderer._render({"graph": graph, "pos": {"n1": (0, 0), "n2": (100, 0)}, "seq": renderer._scan_seq})
+    qa = GraphQaWidget(ctx, renderer)
+
+    # No selection -> every file node in the graph (both nodes share one
+    # file here, so this also proves the path-dedup in _candidate_file_paths).
+    assert qa._candidate_file_paths() == [graph.nodes[0].path]
+
+    renderer._node_items[0].setSelected(True)
+    assert qa._candidate_file_paths() == [graph.nodes[0].path]
+
+
+def test_project_change_clears_the_qa_extraction_cache(ctx, tmp_path):
+    from cowork_local.presentation.graph.graph_qa_widget import GraphQaWidget
+    from cowork_local.presentation.graph.graph_renderer import GraphRenderer
+
+    renderer = GraphRenderer(ctx)
+    qa = GraphQaWidget(ctx, renderer)
+    qa._extract_cache = {"some/path.py": "cached text"}
+
+    renderer.project_changed.emit()
+
+    assert qa._extract_cache == {}
+
+
+def test_qa_collapse_resizes_the_shells_splitter(ctx):
+    """Exact pixel width is Qt's splitter-layout arithmetic, not this code's
+    concern - what matters is that collapsing narrows the QA pane a lot
+    (down near the strip's width) while the strip itself becomes visible and
+    the total splitter width is conserved."""
+    from cowork_local.presentation.graph.structure_graph_view import StructureGraphView
+    from cowork_local.ui.widgets import CollapseStrip
+
+    view = StructureGraphView(ctx)
+    before = view._split.sizes()
+
+    view.qa._set_collapsed(True)
+
+    after = view._split.sizes()
+    assert after[1] <= CollapseStrip.WIDTH + 2
+    assert view.qa.maximumWidth() == CollapseStrip.WIDTH + 2
+    assert sum(after) == sum(before)   # total width conserved, just redistributed
+
+
+def test_hide_event_clears_extracts(ctx):
+    from cowork_local.presentation.graph.structure_graph_view import StructureGraphView
+
+    view = StructureGraphView(ctx)
+    view.qa._extract_cache = {"x": "y"}
+
+    from PySide6.QtGui import QHideEvent
+    view.hideEvent(QHideEvent())
+
+    assert view.qa._extract_cache == {}