Give the content pages the landing's look

Moving from the landing to a page read as changing sites: a narrow
centred column on a flat background, light headings, no cards. The
page now opens like the landing's hero — the same two lights, the same
left edge as the logo, a bold title with the excerpt as its lead — and
the body's headings are bold like every section title on the landing.

The lights move into a shared mixin (ui/_lights.scss) so the hero and
the pages cannot drift apart. On a page they sit on the whole <main>
with `overflow: clip`, so they fade out on their own instead of ending
in a hard edge right where the text starts, and `clip` rather than
`hidden` keeps the sticky side column working.

A side column keeps a page from being a dead end: "keep reading" cards
for the other pages, its own category first, and a card to get in
touch, both on the landing's card surface.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

landing/src/app/core/copy.ts

@@ -90,7 +90,7 @@ export interface Copy {
     closed: string;
   };
   footer: { rights: string; pages: string };
-  page: { back: string; skip: string };
+  page: { skip: string; related: string; ctaTitle: string; ctaLead: string };
   maintenance: { title: string; back: string; until: string };
 }
 
@@ -185,8 +185,10 @@ const es: Copy = {
     pages: 'Más sobre Pireon',
   },
   page: {
-    back: 'Volver al inicio',
     skip: 'Saltar al contenido',
+    related: 'Sigue leyendo',
+    ctaTitle: '¿Hablamos?',
+    ctaLead: 'Si algo de esto encaja con lo que buscas, escríbenos y te respondemos.',
   },
   maintenance: {
     title: 'Estamos de mantenimiento',
@@ -286,8 +288,10 @@ const en: Copy = {
     pages: 'More about Pireon',
   },
   page: {
-    back: 'Back to home',
     skip: 'Skip to content',
+    related: 'Keep reading',
+    ctaTitle: 'Shall we talk?',
+    ctaLead: 'If any of this fits what you are looking for, write to us and we will get back to you.',
   },
   maintenance: {
     title: 'We are under maintenance',
@@ -387,8 +391,10 @@ const ca: Copy = {
     pages: 'Més sobre Pireon',
   },
   page: {
-    back: "Tornar a l'inici",
     skip: 'Salta al contingut',
+    related: 'Continua llegint',
+    ctaTitle: 'En parlem?',
+    ctaLead: "Si alguna cosa d'aquestes encaixa amb el que busques, escriu-nos i et respondrem.",
   },
   maintenance: {
     title: 'Estem de manteniment',