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/sources/registry.py

@@ -93,21 +93,6 @@ def fetch_all(settings: AppSettings) -> list[SourceResult]:
             _close(source)
 
 
-def complete_remote(settings: AppSettings, item: TodoItem) -> tuple[bool, str | None]:
-    """Close a task in its own system. Returns `(did_write, error)`."""
-    sources = build_sources(settings)
-    source = sources.get(item.source)
-    if source is None:
-        return False, None
-    try:
-        return bool(source.complete(item)), None
-    except SourceError as exc:
-        return False, str(exc)
-    finally:
-        for built in sources.values():
-            _close(built)
-
-
 def check_source(settings: AppSettings, name: str) -> tuple[bool, str]:
     """Verify one source's credentials — what the settings page's Test button calls."""
     sources = build_sources(settings)