Removed placeholder data
Added functionality to the insights tab

Flow Tracker v2.1.0 introduces a massive UI overhaul and deeper productivity insights:
- Complete visual redesign featuring a modern, Dieter Rams-inspired glassmorphism aesthetic.
- Granular Session Tagging: You can now tag specific browsing sessions individually (Productive, Distracting, Neutral) rather than just globally tagging a domain.
- Upgraded Insights: Rebuilt the Weekly Heatmap with perfect grid alignment and added hover tooltips to zero-activity time blocks.
- Unified Settings: Consolidated Dark Mode, Data Exporting (CSV/JSON), and History Clearing into a brand new iOS-style Settings modal.