tui.go (1032→164) and tab_sites.go (993→482) violated "small functions"
and "testable in isolation" standards. Extracted 6 new files by concern:
- format.go: pure formatting functions (fmtLatency, fmtUptime, etc.)
- sparkline.go: sparkline rendering (latency, heartbeat, group)
- update.go: Update method decomposed into 15 named handlers
- view_dashboard.go: View, dashboard composition, tab bar, footer
- view_detail.go: site detail panel
- data.go: data refresh with extracted sortSitesForDisplay/filterSites
Added 17 unit tests for the newly-testable pure functions covering
format, sparkline, sort ordering, and filter logic. No behavioral
changes — strict move-and-extract refactor.
