polish: nav scroll threshold, footer cleanup, hero gradient

- Nav: trigger solid background at 10px scroll (was 100px) to prevent logo/text overlap
- Footer: copyright uses legal name "LetsBe Solutions LLC"
- Footer: location changed to "American-founded. Serving the Côte d'Azur and beyond."
- Footer: remove GitHub social link (no public GitHub)
- Hero: smooth gradient fade into trust bar section (no hard color gap)
- Services: "SEO & Digital Marketing" replaces "SEO & Performance"

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/i18n/messages/en.json

@@ -39,7 +39,7 @@
     "title": "Design. Build. Run.",
     "web": {
       "title": "Websites & Web Apps",
-      "features": ["Custom Web Design", "Responsive Development", "SEO & Performance", "Content Management"]
+      "features": ["Custom Web Design", "Responsive Development", "SEO & Digital Marketing", "Content Management"]
     },
     "systems": {
       "title": "Custom Software",
@@ -181,7 +181,7 @@
   },
   "footer": {
     "tagline": "Custom websites, software, and infrastructure for businesses that want to own their digital future.",
-    "location": "Côte d'Azur, France",
+    "location": "American-founded. Serving the Côte d'Azur and beyond.",
     "services": "Services",
     "studio": "Studio",
     "connect": "Connect",

src/i18n/messages/fr.json

@@ -39,7 +39,7 @@
     "title": "Concevoir. Développer. Héberger.",
     "web": {
       "title": "Sites Web & Applications",
-      "features": ["Design Web Sur Mesure", "Développement Responsive", "SEO & Performance", "Gestion de Contenu"]
+      "features": ["Design Web Sur Mesure", "Développement Responsive", "SEO & Marketing Digital", "Gestion de Contenu"]
     },
     "systems": {
       "title": "Logiciels Sur Mesure",
@@ -181,7 +181,7 @@
   },
   "footer": {
     "tagline": "Sites web, logiciels et infrastructure sur mesure pour les entreprises qui veulent maîtriser leur avenir digital.",
-    "location": "Côte d'Azur, France",
+    "location": "Fondé aux États-Unis. Au service de la Côte d'Azur et au-delà.",
     "services": "Services",
     "studio": "Studio",
     "connect": "Contact",