feat: increase photo opacity + add hero photo backgrounds to all pages

- Hero opacity 0.30→0.55, gradient overlay softened (15%/75% vs 30%/60%)
- DifferenceCards photo opacity 0.15→0.40
- ProcessSteps photo opacity 0.15→0.35, removed backdrop-blur
- Added photo backgrounds to 11 hero sections across all pages:
  - planes/en/plans: datacenter-racks
  - servicios/en/servicios: monitor-grafana
  - nosotros/en/about: team-desk-mate
  - contacto/en/contact: hands-typing-coffee
  - preguntas: maldonado-aerial
  - instructivos/en/tutorials: monitor-grafana
- All hero photos at opacity 0.25 with gradient overlay for text readability

src/components/DifferenceCards.astro

@@ -33,7 +33,7 @@ const items = [
       {items.map((item, i) => (
         <article class="glass-card diff-card p-8 flex flex-col relative overflow-hidden" data-diff-index={i}>
           {item.photo && (
-            <div class="absolute inset-0 pointer-events-none" aria-hidden="true" style="opacity: 0.15;">
+            <div class="absolute inset-0 pointer-events-none" aria-hidden="true" style="opacity: 0.40;">
               <img
                 src={`${item.photo}.webp`}
                 alt=""