feat: opt-in conversion layer — GA4 flight analytics, GHL lead capture, ElevenLabs scroll audio

[sbyrd-create]

What

The generated page is currently a beautiful dead end — the finale CTA is href:'#', nothing is measured, nothing is captured. This adds three opt-in, backward-compatible layers to the engine so a shipped scroll-world actually converts. An existing config runs unchanged; every new field defaults off.

1. GA4 flight analytics — analytics:{ ga4, prefix, debug, params }

A scroll-scrubbed page is analytically blind by default (one pageview, no clicks until the end). The engine now emits:

Event	When
sw_scene_view	a section becomes the active scene
sw_scroll_depth	whole-flight depth crosses 25/50/75/100% (once each)
sw_flight_complete	visitor reaches the end (once)
sw_cta_click	any CTA (finale or top bar)
sw_lead_submit	inline capture form posts
sw_audio_toggle	sound toggled

Routed to gtag() when present, else pushed to window.dataLayer (GTM Custom Event triggers). ga4:'G-…' auto-injects gtag; ga4:true reuses an existing snippet.

2. Lead capture on the finale — capture:{…}

• mode:'embed' — drops in a GoHighLevel form/booking iframe (GHL owns submission + routing).
• mode:'inline' — an on-brand form that POSTs name/email/phone + UTM/gclid/fbclid + source/brand/page to a GHL inbound webhook. Honeypot-guarded, required-field checked, no-cors fire-and-trust, success → sw_lead_submit + thank-you (+ optional redirect).
• Security rule stated in-code: the webhook URL is the only (public) credential — no GHL API key ever goes client-side.

3. ElevenLabs scroll audio — audio:{…} + per-section audio:'…mp3'

Per-scene narration/ambient whose volume tracks the scene's opacity, so audio cross-fades with the flight (the audio analogue of the frame-locked seams). Muted until an explicit unmute tap (autoplay policy); never instantiated under prefers-reduced-motion / data-saver (preload:'none' → zero bytes for muted visitors).

Docs

• New references/integrations.md: GA4 event schema + how to read the events as validation gates, GHL setup walk-through (both modes), ElevenLabs encoding recipe, Vercel/framework deploy notes.
• SKILL.md: interview item 7 (ask for conversion wiring — costs zero generations) and Step 9 (conversion & deploy), plus a Step 8 QA bullet.
• index-template.html shows the opt-in config; plugin.json 0.2.0 → 0.3.0; FORK-CHANGES §6.

Why opt-in / compat

Same doctrine as the rest of this fork: every new config field is optional, nothing changes for an upstream config, and the engine stays zero-dependency vanilla JS (the analytics/capture/audio code is ~200 lines inside the same IIFE-scope, namespaced sw- CSS).

Test plan

• node --check on the engine
• In-browser (Chromium): mount clean with all three blocks configured; no console errors
• Inline capture: required-field validation → submit → sw_lead_submit fired + thank-you swap; honeypot field present and hidden
• sw_cta_click (finale CTA), sw_audio_toggle (aria-pressed flips), sw_scene_view on scene change
• data-sw-seo block still hidden on mount
• Scroll-depth threshold logic verified deterministically: 25/50/75/100 fire once each + flight_complete once, idempotent under up/down scrolling
• Base config (no analytics/capture/audio keys) → behavior identical to before; no new DOM, no new requests
• A live GHL webhook end-to-end (needs a real location; the doc walks through mapping + first-lead verification)

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