web-client: formant-weighted radial waveform for speaking state

[sonichi]

Summary

Stacks on merged #338. Makes the 24-bar radial waveform respond to phoneme changes, not just overall amplitude. Top-3 peak bins in the frequency spectrum act as formant proxies (F1/F2/F3); bars within 6 bins of a peak get up to 1.8× their raw height. The ring shape visibly rotates/morphs when the vowel changes ("ahhh" → "eee"), which reads as "the avatar is articulating" rather than "a VU meter next to the avatar."

Why this approach

Converged with @sutando#9708 in #dev today after discussing three scope options:

1. Bump hero avatar to 200–300px and do an SVG overlay — unblocked a bigger hero-screen redesign. Deferred as follow-up.
2. SVG overlay on current avatar sizes — rejected: at 44×44/80×80 an overlay drawn on the image competes with character art at ~5% scale and doesn't visually resolve.
3. Formant-weighted radial waveform ← this PR. Ring lives in the 24–30 radius margin outside the image, proven visible from feat: avatar animation — speaking (green) + working (blue) #338.

What changes

• src/web-client.ts — inside existing startSpeakingDetection() closure: add findPeaks() (linear top-K local-max scan, K=3), and replace the bar-draw loop's val = buf[…]/255 with a formant-weighted value.
• No new deps, no CSS edits, no new files, no asset changes.
• +37/-1 lines total.

Test plan

• npx tsc --noEmit --skipLibCheck clean
• Embedded browser-JS extracted via python and node --check-ed clean (per feedback_web_client_embedded_js_no_ts)
• Manual: hard-refresh, start voice, speak sustained "ahhh" vs "eee" — ring shape visibly differs
• Silence: speaking=false gates the draw — existing behavior preserved (no peaks found → boost=1.0 → raw amplitude → same as today)

Graceful degradation

When the spectrum is low (silence) findPeaks leaves all peakIdx[k] = -1, minDist stays 999, boost = 1.0, val = raw. Output is byte-identical to the pre-PR behavior. If the whole analyser pipeline fails, speaking = false still toggles the border CSS on the <img> — the visor keeps its color animation even without the canvas overlay.

Scope explicitly NOT in this PR

• Full SVG-overlay avatar redesign on a larger hero surface (Option 1 in the scope discussion). MacBook is filing a follow-up issue to track it.
• Working-state redesign (Option G from the research memo). Separate PR if/when owner wants it.

References

• Research memo: notes/avatar-animation-research.md — Option D
• Pre-written spec: notes/avatar-formant-waveform-spec.md
• Two-bot convergence thread: today in #dev

🤖 Generated with Claude Code

[sonichi]

MacBook review: LGTM. Clean formant extraction — top-3 peak detection with proximity-weighted boost. The 6-bin radius and 0.8 max boost factor are reasonable defaults. No TS-in-JS mistakes this time. Merge when ready.