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_schedule_task_tab.py

@@ -0,0 +1,125 @@
+"""EPIC R08-T11: ScheduleTaskTab shell + KanbanBoardWidget, real Qt offscreen.
+
+Drives the real widgets end to end (build -> refresh -> drag-drop rule via
+TaskApplicationService -> refresh) against a tmp_path task repository, the
+way ``test_history_dir_race.py`` proves R06-T04 against real Qt rather than
+a double. ``TaskApplicationService``'s own business rules are already unit
+tested (R07-T04); this file exists to prove the WIDGET is actually wired to
+that service, not to re-test the rules themselves.
+"""
+from __future__ import annotations
+
+import os
+from pathlib import Path
+
+import pytest
+
+os.environ.setdefault("QT_QPA_PLATFORM", "offscreen")
+
+from cowork_local.config import AppConfig  # noqa: E402
+from cowork_local.infrastructure.persistence.json.task_repository_impl import (  # noqa: E402
+    TaskRepository,
+)
+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: Path):
+    return AppContext(AppConfig.load(tmp_path / "config.json"))
+
+
+@pytest.fixture
+def tasks_dir(tmp_path: Path) -> Path:
+    d = tmp_path / "tasks"
+    d.mkdir()
+    return d
+
+
+def test_schedule_task_tab_builds_and_refreshes_with_no_tasks(ctx, tasks_dir):
+    from cowork_local.presentation.scheduling.schedule_task_tab import ScheduleTaskTab
+
+    tab = ScheduleTaskTab(ctx, scheduler=None, tasks_dir=tasks_dir)
+    tab.refresh()   # must not raise against an empty repo
+
+    assert tab.kanban.columns.keys()   # 7 lanes were built
+
+
+def test_kanban_renders_a_task_into_its_status_lane(ctx, tasks_dir):
+    from cowork_local.presentation.scheduling.kanban_board_widget import KanbanBoardWidget
+
+    repo = TaskRepository(tasks_dir)
+    task = repo.create("My Task", task_type="cowork")
+    task["status"] = "backlog"
+    repo.save(task)
+
+    board = KanbanBoardWidget(ctx, tasks_dir=tasks_dir)
+    board.refresh()
+
+    from PySide6.QtCore import Qt
+
+    backlog_ids = [board.columns["backlog"].item(i).data(Qt.UserRole)
+                   for i in range(board.columns["backlog"].count())]
+    assert task["task_id"] in backlog_ids
+
+
+def test_dropping_a_card_on_done_disables_its_schedule_through_the_real_widget(ctx, tasks_dir):
+    """Same rule TaskApplicationService.move_to_status covers at the unit
+    level (R07-T04) — this proves the Kanban widget's drop handler actually
+    calls it, end to end, with a real TaskRepository on disk."""
+    from cowork_local.presentation.scheduling.kanban_board_widget import KanbanBoardWidget
+
+    repo = TaskRepository(tasks_dir)
+    task = repo.create("Recurring", task_type="cowork")
+    task["schedule"]["enabled"] = True
+    task["schedule"]["run_at"] = "2026-08-28 09:00"
+    task["schedule"]["repeat_type"] = "daily"
+    task["status"] = "scheduled"
+    repo.save(task)
+
+    board = KanbanBoardWidget(ctx, tasks_dir=tasks_dir)
+    board.refresh()
+
+    board._on_task_dropped(task["task_id"], "done")
+
+    on_disk = repo.get(task["task_id"])
+    assert on_disk["status"] == "done"
+    assert on_disk["schedule"]["enabled"] is False
+
+
+def test_kanban_edit_requested_is_wired_to_the_shells_edit_task(ctx, tasks_dir, monkeypatch):
+    """Proves ScheduleTaskTab actually connects
+    ``kanban.edit_requested -> self._edit_task`` (not just that the Kanban
+    widget emits the signal in isolation) by monkeypatching the dialog class
+    ``_edit_task`` opens and checking it was constructed for the right task."""
+    import cowork_local.ui.task_editor_dialog as task_editor_dialog_module
+    from cowork_local.presentation.scheduling.schedule_task_tab import ScheduleTaskTab
+
+    repo = TaskRepository(tasks_dir)
+    task = repo.create("Editable")
+    repo.save(task)
+
+    seen_task_ids = []
+
+    class _FakeDialog:
+        def __init__(self, task, all_tasks, parent, ctx):
+            seen_task_ids.append(task["task_id"] if task else None)
+            self.edited_task = None
+
+        def exec(self):
+            return False   # Cancel — nothing further should happen
+
+    monkeypatch.setattr(task_editor_dialog_module, "TaskEditorDialog", _FakeDialog)
+
+    tab = ScheduleTaskTab(ctx, scheduler=None, tasks_dir=tasks_dir)
+    tab.kanban.edit_requested.emit(task["task_id"])
+
+    assert seen_task_ids == [task["task_id"]]