[WIP] Update statistics display to separate by activity type

[Copilot]

• Inspect repository structure and baseline validation commands
• Run baseline lint/build to identify pre-existing issues
• Update StatsGrid.tsx reduce logic to compute stats by activity type
• Add a simple All/Run/Ride/Swim filter control above stats cards in existing visual style
• Add/adjust focused tests if test infrastructure exists (or skip if none)
• Run targeted lint/type validation for changed files
• Manually verify UI behavior and capture a screenshot
• Run security scan (codeql_checker) and finalize