perf(ui): defer results fetch to render-eligible ticks

[alexpasmantier]

Summary

• Television::update() was running the full results pipeline (matcher lock, index computation, per-item to_string + clone) on every tick (~50 Hz), while the renderer only consumes new state at ~17 Hz under load and ~2 Hz idle. Under heavy load (large source streams, big corpora) the redundant work starves keystrokes and renders.
• Now the results pipeline only runs on render-eligible ticks. Counts are refreshed every tick via a new cheap Matcher::update_counts() so select_1 / take_1 / status bar stay accurate.

Test plan

• tv files or find ~ -type f | tv on a large tree — UI stays responsive while loading; typing feels snappier
• select_1 / take_1 / take_1_fast flows still trigger correctly