Add hero CTA A/B test (hero_cta: control vs free_emphasis)

Sticky 50/50 variant assignment via gw_ab_hero cookie, server-rendered
so no flicker. Tracks exposures, CTA clicks, and booking conversions
to ab_events (table self-creates on first POST). Bot UAs are dropped;
exposures/clicks dedupe per session.

- ?ab=control / ?ab=free_emphasis forces and persists a variant
- /owner/experiments shows per-variant CVR and relative lift
- AB only runs on the marketing surface

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/lib/components/BookingWizard.svelte

@@ -4,12 +4,14 @@
   import Icon from '$lib/components/Icon.svelte';
   import { reveal } from '$lib/actions/reveal';
   import type { BookingContent } from '$lib/types';
+  import { trackAb, type AbContext } from '$lib/ab';
 
   type SuccessModalComponentType = typeof import('$lib/components/SuccessModal.svelte').default;
   type ErrorModalComponentType = typeof import('$lib/components/ErrorModal.svelte').default;
 
   export let booking: BookingContent;
   export let pagePath = '';
+  export let ab: AbContext | undefined = undefined;
   $: isCompactContactPage = pagePath === '/contact-us';
 
   const defaultServices = ['Tiny Gang Pack Walks', 'Solo Walks', 'Puppy Visits', 'Other Services'];
@@ -285,6 +287,7 @@
       }
 
       submitted = true;
+      if (ab) trackAb({ ...ab, event_type: 'conversion', meta: { surface: 'booking_submit' } });
     } catch (err: unknown) {
       submitErrorDetail = err instanceof Error ? err.message : String(err);
       showErrorModal = true;

src/lib/components/HeroSection.svelte

@@ -1,9 +1,23 @@
 <script lang="ts">
+  import { onMount } from 'svelte';
   import Icon from '$lib/components/Icon.svelte';
   import type { CallToAction, HeroContent } from '$lib/types';
+  import { trackAb, type AbContext } from '$lib/ab';
 
   export let hero: HeroContent;
   export let reviewCta: CallToAction | undefined = undefined;
+  export let primaryCtaOverride: CallToAction | undefined = undefined;
+  export let ab: AbContext | undefined = undefined;
+
+  $: primaryCta = primaryCtaOverride ?? hero.primaryCta;
+
+  onMount(() => {
+    if (ab) trackAb({ ...ab, event_type: 'exposure', meta: { surface: 'hero' } });
+  });
+
+  function handlePrimaryCtaClick() {
+    if (ab) trackAb({ ...ab, event_type: 'cta_click', meta: { surface: 'hero_primary' } });
+  }
 
   $: titleParts = splitTitle(hero.title);
   $: mobileTitle = hero.mobileTitle?.trim() || `${hero.title} ${hero.highlight}`.trim();
@@ -133,12 +147,13 @@
 
       <div class="hero-buttons">
         <a
-          href={hero.primaryCta.href}
-          target={linkTarget(hero.primaryCta.external)}
-          rel={linkRel(hero.primaryCta.external)}
+          href={primaryCta.href}
+          target={linkTarget(primaryCta.external)}
+          rel={linkRel(primaryCta.external)}
           class="btn btn-yellow btn-with-arrow btn-hide-arrow-mobile"
+          on:click={handlePrimaryCtaClick}
         >
-          {hero.primaryCta.label}
+          {primaryCta.label}
           <Icon name="fas fa-arrow-right" />
         </a>
         <a