Two PLN UX fixes from auditioning the loops panel:
1. Chops were way too short (0.06 s slices = clicks, not cuts). analyze_chops now
floors at min_len_s=0.25 and extends to onset→skip-two for phrase-length options;
vocal chops now land 0.29–1.07 s (verified) — actual word/phrase chops.
2. A 10+ vertical list was impractical to navigate. Replaced it with a TIMELINE
overview (the research §6 design): every candidate is placed on the track by its
start/length, coloured by lead stem, height + opacity by score — so you SEE where
the candidates are at a glance and click one to focus. Below sits a single detail
panel (stems, waveforms, audition, keep-toggles, Forge) for the selected candidate,
plus prev/next stepping and a "candidate N / M" counter. Scannable map + one
focused editor instead of a scroll-wall.
Verified in Chromium: 8 segments render, click-to-focus (candidate 1→4), prev/next,
no console errors; stem durations now display (the HTTP/1.1 + preload audio fix shows
2:43). Works for loops and chops modes (header reads "N-bar" or "chop · Ns").
