feat(R07): task repository, schedule calculator, Qt clock adapter, task/AI-planner services

Team Hoa, EPIC R07 (Scheduling & Workflow Runtime) - Team Hoa scope only
(R07-T01 -> T05; R07-T06 Co4EWorkflowService is Team Nam's).

- R07-T01: infrastructure/persistence/json/task_repository_impl.py wraps
  core/tasks.py's CRUD; core/tasks.py::save_task now writes through
  atomic_write.write_json (same durability fix as R06-T02, save_task was
  still doing a plain write_text).
- R07-T02: domain/tasks/schedule_calculator.py::ScheduleCalculator - the
  cron/interval/daily/weekly/monthly due-time math extracted from
  core/tasks.py, pure Python with is_holiday/make_cron injected so domain/
  never imports core (ADR-001 I2). core/tasks.py keeps its old function
  names as thin wrappers so every existing caller is unchanged. This was
  previously untested; now has its own unit suite.
- R07-T03: infrastructure/qt/qt_scheduler_clock.py::QtSchedulerClock wraps
  the QTimer TaskScheduler used to own directly, injected via a new
  `clock=` constructor param (defaults to a real one). Originally planned
  at platform/qt/... ; moved after confirming that name shadows the
  stdlib platform module (used by core/windows_sandbox_vm.py,
  core/appcontainer_sandbox.py) whenever the repo root is on sys.path.
  tests/fakes/fake_clock.py lets scheduler dispatch be tested tick-by-tick
  with no Qt event loop.
- R07-T04: application/scheduling/task_application_service.py centralizes
  run_now/duplicate/pause/delete/bulk_delete and the Kanban drag-drop
  business rules (move_to_status), currently only reachable by driving
  the real ui/schedule_task_tab.py widget.
- R07-T05: application/scheduling/ai_task_planner_service.py wraps
  core/ai_task_planner.py::plan_tasks and core/task_import.py::import_tasks
  as a seam, plus the attachment-stamping step that used to only exist
  inside the AI-create dialog's worker closure.

pytest: 328 pass (same 4 pre-existing failures as the R05/R06 baseline,
unrelated to this work - see docs/refactor/BaoCao_TeamHoa_R05_R06.md).
scripts/check_imports.py: PASS.

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

tests/integration/test_qt_scheduler_clock.py

@@ -0,0 +1,53 @@
+"""EPIC R07-T03: QtSchedulerClock against a REAL QTimer/event loop.
+
+``tests/unit/test_task_scheduler_dispatch.py`` covers ``TaskScheduler``'s
+dispatch logic entirely through ``tests/fakes/fake_clock.py::FakeClock`` (no
+Qt at all — that's the whole point of the extraction). This file is the
+complement: it proves the adapter itself actually drives a real ``QTimer``
+and pumps a real event loop, offscreen, the way ``test_history_dir_race.py``
+proves ``ui/chat_panel.py``'s fix against real Qt rather than a double.
+"""
+from __future__ import annotations
+
+import os
+
+os.environ.setdefault("QT_QPA_PLATFORM", "offscreen")
+
+import pytest  # noqa: E402
+
+from PySide6.QtTest import QTest  # noqa: E402
+from PySide6.QtWidgets import QApplication  # noqa: E402
+
+from cowork_local.infrastructure.qt.qt_scheduler_clock import QtSchedulerClock  # noqa: E402
+
+
+@pytest.fixture(scope="module")
+def qapp():
+    return QApplication.instance() or QApplication([])
+
+
+def test_start_fires_callback_on_the_real_qt_event_loop(qapp):
+    clock = QtSchedulerClock()
+    ticks = []
+    clock.start(interval_ms=10, callback=lambda: ticks.append(1))
+    try:
+        QTest.qWait(200)   # let the real QTimer fire a few times
+    finally:
+        clock.stop()
+    assert len(ticks) >= 1
+
+
+def test_stop_prevents_further_callbacks(qapp):
+    clock = QtSchedulerClock()
+    ticks = []
+    clock.start(interval_ms=10, callback=lambda: ticks.append(1))
+    QTest.qWait(50)
+    clock.stop()
+    count_after_stop = len(ticks)
+    QTest.qWait(100)
+    assert len(ticks) == count_after_stop   # no more callbacks after stop()
+
+
+def test_pump_processes_pending_events_without_raising(qapp):
+    clock = QtSchedulerClock()
+    clock.pump()   # must not raise even with nothing pending