refactor: enhance TimerPage layout and functionality; update theme and tokens for improved design consistency

- Refactored TimerPage component to improve layout and user experience.
- Updated theme configuration to utilize design tokens for better maintainability.
- Introduced new tokens for colors and typography to align with design principles.
- Simplified state management and improved timer functionality.
- Enhanced accessibility and responsiveness of UI elements.

backend/app/models.py

@@ -90,9 +90,12 @@ class PomodoroSession(Base):
 class TaskRecord(Base):
     """A todo item, wherever it came from.
 
-    External tasks are cached here on every refresh so the UI is instant and the
-    daily report still works when Jira is down. Locally created tasks live here
-    too, with `source = "local"` — they are the only ones we own outright.
+    External tasks are mirrored here on every refresh so the UI is instant and
+    the daily report still works when Jira is down. Locally created tasks live
+    here too, with `source = "local"`.
+
+    Completion is never recorded from this app: you close a task where it lives,
+    and the next refresh notices. That keeps one source of truth per task.
     """
 
     __tablename__ = "tasks"
@@ -119,8 +122,12 @@ class TaskRecord(Base):
     is_done: Mapped[bool] = mapped_column(Boolean, default=False, index=True)
     completed_at: Mapped[datetime | None] = mapped_column(DateTime(timezone=True))
     completed_date: Mapped[date | None] = mapped_column(Date, index=True)
-    completed_here: Mapped[bool] = mapped_column(Boolean, default=False)
-    """True when *this app* closed it — what the daily report counts."""
+    """The day the task was seen to close, in your timezone.
+
+    Tasks are never ticked off here — Jira, Todoist and Google Tasks own that —
+    so this is set when a refresh finds a task closed, or finds it gone from a
+    source that was otherwise healthy. That is what the daily report counts.
+    """
 
     estimated_pomodoros: Mapped[int | None] = mapped_column(Integer)
     pinned: Mapped[bool] = mapped_column(Boolean, default=False)