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/graph_scene_items.py

@@ -0,0 +1,142 @@
+"""Native QGraphicsScene primitives for the fallback (non-WebEngine) graph
+view (R08-T14, split out of ``graph_renderer.py`` to keep it under the
+400-line cap; originally ``ui/structure_graph_view.py``, lines 65-186 of the
+original 1035-line file: ``_Bridge``, ``_Edge``, ``_Node``, ``_GraphView``).
+"""
+from __future__ import annotations
+
+import math
+
+from PySide6.QtCore import QObject, QPointF, Qt, Slot
+from PySide6.QtGui import QBrush, QColor, QFont, QPen
+from PySide6.QtWidgets import QGraphicsEllipseItem, QGraphicsLineItem, QGraphicsSimpleTextItem, QGraphicsView
+
+from cowork_local.core.structure_graph import EDGE_KIND_COLORS, NODE_KIND_COLORS
+from cowork_local.theme import current_palette
+from cowork_local.ui.osutil import open_folder, open_location
+
+
+class _Bridge(QObject):
+    """Exposed to the D3 page so a Shift+click on a node can open its
+    storage folder/link (local path or URL — see osutil.open_location)."""
+
+    @Slot(str)
+    def openPath(self, path: str) -> None:  # noqa: N802 - JS-facing name
+        if path:
+            open_location(path)
+
+
+class _Edge(QGraphicsLineItem):
+    def __init__(self, a: "_Node", b: "_Node", type_: str = ""):
+        super().__init__()
+        self.a, self.b = a, b
+        self.type = type_
+        # Colour the edge by its RELATIONSHIP type (contains/defines/method/…),
+        # so the graph shows what each connection MEANS — falling back to the
+        # source node's tint for any untyped edge.
+        color = QColor(EDGE_KIND_COLORS.get(type_, "")) if type_ else QColor()
+        if not color.isValid():
+            color = a.brush().color().lighter(130)
+        self._color = color
+        self.setPen(QPen(color, 1.4))
+        self.setZValue(-1)
+        # A small label naming the relationship, shown at the edge midpoint.
+        self._label = None
+        if type_:
+            self._label = QGraphicsSimpleTextItem(type_, self)
+            self._label.setBrush(QBrush(color.lighter(140)))
+            f = QFont()
+            f.setPointSize(7)
+            self._label.setFont(f)
+            self._label.setZValue(0)
+        a.edges.append(self)
+        b.edges.append(self)
+        self.adjust()
+
+    def adjust(self) -> None:
+        pa, pb = self.a.scenePos(), self.b.scenePos()
+        self.setLine(pa.x(), pa.y(), pb.x(), pb.y())
+        if self._label is not None:
+            br = self._label.boundingRect()
+            self._label.setPos((pa.x() + pb.x()) / 2 - br.width() / 2,
+                                (pa.y() + pb.y()) / 2 - br.height() / 2)
+
+
+class _Node(QGraphicsEllipseItem):
+    def __init__(self, data, radius: int):
+        super().__init__(-radius, -radius, 2 * radius, 2 * radius)
+        self.data = data
+        self.edges = []
+        tok = current_palette()
+        # NODE_KIND_COLORS is a categorical data encoding (one hue per node
+        # kind), not UI chrome — it stays fixed across themes on purpose so a
+        # given kind is always the same colour. Only the chrome follows tokens.
+        color = QColor(NODE_KIND_COLORS.get(data.kind, tok.text_muted))
+        self.setBrush(QBrush(color))
+        self.setPen(QPen(color.darker(160), 1.5))
+        self.setFlags(
+            QGraphicsEllipseItem.ItemIsMovable
+            | QGraphicsEllipseItem.ItemIsSelectable
+            | QGraphicsEllipseItem.ItemSendsGeometryChanges
+        )
+        self.setZValue(1)
+        label = QGraphicsSimpleTextItem(data.label, self)
+        label.setBrush(QBrush(QColor(tok.text)))
+        label.setPos(radius + 3, -8)
+
+    def itemChange(self, change, value):  # noqa: N802
+        if change == QGraphicsEllipseItem.ItemPositionHasChanged:
+            for edge in self.edges:
+                edge.adjust()
+        return super().itemChange(change, value)
+
+
+class _GraphView(QGraphicsView):
+    def __init__(self, scene):
+        super().__init__(scene)
+        self.setDragMode(QGraphicsView.NoDrag)
+        self._panning = False
+        self._pan_start = QPointF()
+
+    def wheelEvent(self, e):  # noqa: N802
+        self.scale(1.15 if e.angleDelta().y() > 0 else 1 / 1.15,
+                   1.15 if e.angleDelta().y() > 0 else 1 / 1.15)
+
+    def mousePressEvent(self, e):  # noqa: N802
+        if e.button() == Qt.LeftButton and self.itemAt(e.pos()) is None:
+            self._panning = True
+            self._pan_start = e.position()
+            self.setCursor(Qt.ClosedHandCursor)
+            e.accept()
+            return
+        super().mousePressEvent(e)
+
+    def mouseMoveEvent(self, e):  # noqa: N802
+        if self._panning:
+            delta = e.position() - self._pan_start
+            self._pan_start = e.position()
+            self.horizontalScrollBar().setValue(int(self.horizontalScrollBar().value() - delta.x()))
+            self.verticalScrollBar().setValue(int(self.verticalScrollBar().value() - delta.y()))
+            e.accept()
+            return
+        super().mouseMoveEvent(e)
+
+    def mouseReleaseEvent(self, e):  # noqa: N802
+        if self._panning:
+            self._panning = False
+            self.setCursor(Qt.ArrowCursor)
+            e.accept()
+            return
+        super().mouseReleaseEvent(e)
+
+    def mouseDoubleClickEvent(self, e):  # noqa: N802
+        """Double-click or Ctrl+click on a node opens its storage folder."""
+        item = self.itemAt(e.pos())
+        if isinstance(item, _Node) and getattr(item.data, "path", ""):
+            open_folder(item.data.path)
+            e.accept()
+            return
+        super().mouseDoubleClickEvent(e)
+
+
+__all__ = ["_Bridge", "_Edge", "_Node", "_GraphView"]