Audio Wave: segments = user splits only (721 groups are markers, not segments)

Per clarification: the 721 group lines are clip markers, NOT segments. Segments come
ONLY from user split points, numbered globally from 1 — so the first split is seg1, not
seg23. 0 splits = 0 segments; N splits = N segments (seg k = point k-1 .. split k, tail
after the last split excluded). group lines still drawn (bold) + used for the group#.
JS matches (segPoints/nSegs). Empty summary now prompts to add splits.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

nodes/audio_guide.py

@@ -180,6 +180,9 @@ def _render(rms_n, times, duration, beats, bounds, segs,
 
 
 def _summary(duration, sr, bpm, beats, segs, global_notes):
+    if not segs:
+        return (f"AUDIO GUIDE — {duration:.2f}s clip. No segments defined yet: double-click "
+                f"the waveform to add split points (each split starts a new beat).")
     lines = ["AUDIO GUIDE — align the video beats to this audio:",
              f"- duration: {duration:.2f}s  |  sample_rate: {sr} Hz"]
     if bpm: