281 gap skipping fixes

[maboa]

Summary

Four small fixes around gap-skip so the feature feels live instead of stale. Addresses #281 and #284

1. Carry settings across to new transcripts (483ef62)

registerStrikeThrus (which rebuilds audioDataArray and re-attaches skip listeners against the
current transcript and gap settings) was only bound to hyperaudioTranscriptLoaded, which only the
localStorage load path dispatches. Deepgram, Whisper, and JSON/SRT/VTT import dispatch hyperaudioInit
instead, so the skip pipeline kept pointing at the previous transcript's word data.

Fix: bind registerStrikeThrus to hyperaudioInit as well. The two events are disjoint, so no
double-fire.

2. Labeled-units format for the savings line (28e3507)

"Playback shortened by 3725.4 seconds" doesn't scale well past a minute. Sub-minute savings still render
as 12.3 seconds (decimal preserved), but from 60s upward it switches to labeled units that drop zero
components: 1m 30s, 1h 2m 5s, 1h.

3. Recalculate on transcript edits and new transcripts (a2c43b6)

• Call updateGapSavingsMessage() from registerStrikeThrus so the "Playback shortened by X" line
  reflects the new transcript on every rebuild (transcribe / import / localStorage load / strikethrough
  toggle).
• Add a debounced input listener delegated on document that calls registerStrikeThrus after 150ms
  of edit inactivity on #hypertranscript. Deleting a word turns its time slot into a gap, which should
  be reflected in both the skip pipeline and the savings message. Delegated on document so the listener
  survives transcript element replacement via restoreTranscript.

4. Keep the karaoke highlight in sync (4983b0e)

The hyperaudio-lite library tracks the active word via a cached wordArr and a chained setTimeout
that polls currentTime, but it only natively listens for play/pause — not seeked or DOM
mutations. That leaves two windows where the highlight freezes:

• After edits: the polling chain crashes silently if it touches a now-detached span
  (word.n.parentNode is null, .classList throws inside the setTimeout callback), and nothing
  restarts it.
• After a gap skip: our code calls myPlayer.currentTime = nextStart + 0.05 directly; the library
  has no idea we jumped and waits for its stale timer to fire seconds later before relocating the active
  word.

Fix: a refreshHyperaudioInstance() helper rebuilds wordArr and parentElements, updates the visual
state, and kicks checkPlayHead to restart the polling chain. Called from registerStrikeThrus so
edits and new transcripts both refresh the library's caches. Also kick checkPlayHead from
checkStrikeThrus right after a gap skip so the highlight resyncs to the post-skip word immediately
rather than waiting for the stale timer.

Test plan

• Enable gap-skip with custom threshold/buffer. Transcribe a new file via Deepgram → confirm skips
  fire and the savings line updates.
• Same flow via Whisper.
• Same flow via JSON/SRT/VTT import.
• Load a saved session from localStorage → confirm skips still work and the savings line is correct.
• Delete a word in the transcript while gap-skip is on → confirm within ~150ms the savings line
  updates and the new gap (the deleted word's slot) is skipped on playback.
• Confirm karaoke highlight follows playback continuously across deletions (no freeze on the last
  edited word).
• Confirm karaoke highlight follows playback continuously across gap skips (no freeze at the start
  of the gap).
• Confirm savings line shows X.X seconds under 60s, Xm Ys between 1–59 min, Xh Ym Zs for ≥ 1h.