1.3 - Whole-window burn rate

What's Changed

• feat: span whole window in burn-rate sparkline by @LLawli in #8

The burn-rate sparkline now covers the entire elapsed session window instead of just the last few minutes. For the 7-day view each bar groups roughly an hour, so you finally see the whole week's burn at a glance; the 5h view shows the full session too. The avg/peak captions already reflected the full window.

Full Changelog: 1.2...1.3