feat(ads): wire Meta Pixel for ad attribution

Pixel ID 1904240520247944 (sase.tr) created on ad account
act_1227112768351770. Lazy-injected like PostHog so it stays off
when VITE_META_PIXEL_ID is unset. Tracks PageView on every route
change, CompleteRegistration on email/Google signup, and
InitiateCheckout on Stripe button click (value in TRY).

Coolify env: set VITE_META_PIXEL_ID=1904240520247944 before next
deploy so it gets baked into the Vite build.

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

docker-compose.coolify.yml

@@ -7,6 +7,7 @@ services:
         - VITE_FARO_ENABLED=${VITE_FARO_ENABLED:-false}
         - VITE_FARO_COLLECTOR_URL=${VITE_FARO_COLLECTOR_URL:-}
         - VITE_POSTHOG_KEY=${VITE_POSTHOG_KEY:-}
+        - VITE_META_PIXEL_ID=${VITE_META_PIXEL_ID:-}
     environment:
       - NODE_ENV=production
       - PORT=4000