fix(css): constrain gallery heading and pricing/contact sections to main container width

- Gallery .section-head now uses the same 1400px container + 1.5rem
  horizontal padding as .masonry-grid, so 'PHOTO GALLERY' / 'A look inside'
  align flush with the leftmost image edge (24px gutter) instead of sitting
  at the very left of the page.
- .pricing-section and .contact-section are now constrained to
  max-width: 1200px and centered (matching .floors-section and .lage-section),
  so the 'Mietkonditionen' (dark) and 'Kontakt' (cream) blocks no longer
  span the full viewport.
- Mobile: matching padding adjustment for the new .section-head rule at
  width <= 768px.

public/css/haus-schleusingen.css

@@ -548,6 +548,12 @@ nav.scrolled {
   margin: 0 auto;
 }
 
+.gallery-section .section-head {
+  max-width: 1400px;
+  margin: 0 auto;
+  padding: 5rem 1.5rem 2.5rem;
+}
+
 .gallery-header h2 {
   font-family: "Cormorant Garamond", serif;
   font-size: clamp(2rem, 3vw, 2.8rem);
@@ -636,6 +642,10 @@ nav.scrolled {
   .gallery-header {
     padding: 3rem 1.5rem 2rem;
   }
+
+  .gallery-section .section-head {
+    padding: 3rem 1rem 2rem;
+  }
 }
 
 @media (width <= 480px) {
@@ -789,6 +799,8 @@ nav.scrolled {
 .pricing-section {
   background: var(--dark);
   padding: 6rem 3rem;
+  max-width: 1200px;
+  margin: 0 auto;
 }
 
 .pricing-inner {
@@ -1044,6 +1056,8 @@ nav.scrolled {
 .contact-section {
   background: var(--cream);
   padding: 6rem 3rem;
+  max-width: 1200px;
+  margin: 0 auto;
 }
 
 .contact-inner {