The DevIndex grid heatmap correctly displayed 2026, but the Activity sparkline was missing it. Additionally, the 'Activity (15y)' header was hardcoded and inaccurate.

Changes:

1. Restore 2026: Ensure both Heatmap and Sparkline loops include the current year ().
2. Dynamic Header: Calculate the activity duration dynamically (e.g., 'Activity (17y)') based on the start year (2010) and current year.
3. Future-Proofing: Replace hardcoded '2025' limits with dynamic current year logic.