feat(analytics): pull pm86 site-id from CMS page_config, drop env var

- +layout.server: expose pageConfig.analyticsPm86SiteId on layout data
- +layout.svelte: inject analytics.pm86.de script when CMS value present
- +error.svelte: light 404 page with wald-700 accent, dropped dark gradient
- .env.example + deploy.yml: remove PUBLIC_ANALYTICS_PM86_SITE_ID

src/routes/+layout.svelte

@@ -126,11 +126,11 @@
       data-website-id={import.meta.env.PUBLIC_UMAMI_WEBSITE_ID}
     ></script>
   {/if}
-  {#if import.meta.env.PUBLIC_ANALYTICS_PM86_SITE_ID}
+  {#if data.analyticsPm86SiteId}
     <script
       defer
       src="https://analytics.pm86.de/api/script.js"
-      data-site-id={import.meta.env.PUBLIC_ANALYTICS_PM86_SITE_ID}
+      data-site-id={data.analyticsPm86SiteId}
     ></script>
   {/if}
   {#if formbricksScript}