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>

presentation/graph/structure_graph_view.py

@@ -0,0 +1,80 @@
+"""StructureGraphView shell (R08-T14) — assembles
+``graph_renderer.py::GraphRenderer`` and
+``graph_qa_widget.py::GraphQaWidget`` behind the splitter that used to be
+inline in ``ui/structure_graph_view.py::StructureGraphView.__init__`` (lines
+188-343 of the original 1035-line file), and forwards the public methods
+``app.py``/``ui/workspace_tab.py`` call: ``schedule_rescan``,
+``auto_scan_and_fit``, ``set_project``, ``prewarm``.
+"""
+from __future__ import annotations
+
+from PySide6.QtCore import Qt, Signal
+from PySide6.QtWidgets import QSplitter, QVBoxLayout, QWidget
+
+from cowork_local.i18n import on_language_changed
+from cowork_local.presentation.graph.graph_qa_widget import GraphQaWidget
+from cowork_local.presentation.graph.graph_renderer import GraphRenderer
+from cowork_local.state import AppContext
+from cowork_local.ui.widgets import CollapseStrip
+
+_COLLAPSED_SIZES_HINT = (840, 320)   # matches the original single-class default
+
+
+class StructureGraphView(QWidget):
+    status_message = Signal(str)
+
+    def __init__(self, ctx: AppContext):
+        super().__init__()
+        self.ctx = ctx
+
+        root = QVBoxLayout(self)
+        self.renderer = GraphRenderer(ctx)
+        self.renderer.status_message.connect(self.status_message.emit)
+        self.qa = GraphQaWidget(ctx, self.renderer)
+        self.qa.status_message.connect(self.status_message.emit)
+        self.qa.collapse_changed.connect(self._on_qa_collapse_changed)
+
+        self._split = QSplitter(Qt.Horizontal)
+        self._split.addWidget(self.renderer)
+        self._split.addWidget(self.qa)
+        self._split.setChildrenCollapsible(False)
+        self._split.setSizes(list(_COLLAPSED_SIZES_HINT))
+        root.addWidget(self._split, 1)
+
+        on_language_changed(self._retranslate)
+
+    def _retranslate(self) -> None:
+        self.renderer._retranslate()
+        self.qa.retranslate()
+
+    def _on_qa_collapse_changed(self, collapsed: bool) -> None:
+        strip_w = CollapseStrip.WIDTH + 2
+        if collapsed:
+            self.qa.setMaximumWidth(strip_w)
+            sizes = self._split.sizes()
+            if len(sizes) == 2:
+                self._split.setSizes([max(1, sum(sizes) - strip_w), strip_w])
+        else:
+            self.qa.setMaximumWidth(16777215)
+            self._split.setSizes(list(_COLLAPSED_SIZES_HINT))
+
+    # ---- public API (app.py / ui/workspace_tab.py) --------------------------- #
+    def schedule_rescan(self, path: str = "") -> None:
+        self.renderer.schedule_rescan(path)
+
+    def auto_scan_and_fit(self) -> None:
+        self.renderer.auto_scan_and_fit()
+
+    def set_project(self, project_id: str) -> None:
+        self.renderer.set_project(project_id)
+
+    def prewarm(self) -> None:
+        self.renderer.prewarm()
+
+    def hideEvent(self, e):  # noqa: N802
+        # Leaving the GraphRAG tab → drop the temporary extracted info.
+        self.qa.clear_extracts()
+        super().hideEvent(e)
+
+
+__all__ = ["StructureGraphView"]