feat: background photo system — random Lanzarote landscapes behind CV grid

Dev-only toggle button enables/disables photo backgrounds. Photos are
auto-discovered from static/images/backgrounds/ and randomly selected
on each page load. Production is unaffected — no button, no photo.

static/css/01-foundation/_reset.css

@@ -12,23 +12,25 @@
 /* Body base */
 body {
   background-color: var(--page-bg, #d6d6d6);
-
-  /* OLD PATTERN - Keep for reference (can be restored anytime) */
-  /* background-image:
-    linear-gradient(90deg, rgba(0, 0, 0, 0.05) 1px, transparent 1px),
-    linear-gradient(180deg, rgba(0, 0, 0, 0.05) 1px, transparent 1px),
-    linear-gradient(90deg, rgba(0, 0, 0, 0.02) 1px, transparent 1px),
-    linear-gradient(180deg, rgba(0, 0, 0, 0.02) 1px, transparent 1px);
-  background-size: 50px 50px, 50px 50px, 10px 10px, 10px 10px; */
-
-  /* NEW TEST PATTERNS - Theme-specific (woven fabric for light, diagonal grid for dark) */
   background-image: var(--page-bg-pattern, none);
-  background-size: 40px 40px; /* For dark theme diagonal grid */
+  background-size: 40px 40px;
   background-attachment: fixed;
   max-width: 100vw; /* Prevent horizontal overflow */
   overflow-x: clip; /* Clip prevents horizontal scroll WITHOUT breaking position: sticky */
 }
 
+/* Background photo layer — activated via JS in dev mode */
+body.bg-photo {
+  background-image:
+    var(--page-bg-pattern, none),
+    linear-gradient(var(--page-bg-tint, rgba(214,214,214,0.85)), var(--page-bg-tint, rgba(214,214,214,0.85))),
+    var(--bg-photo-url, none);
+  background-size: auto, auto, cover;
+  background-position: 0 0, 0 0, center;
+  background-repeat: repeat, repeat, no-repeat;
+  background-attachment: fixed;
+}
+
 /* Smooth scrolling */
 html {
   scroll-behavior: smooth;

static/css/01-foundation/_themes.css

@@ -62,6 +62,9 @@
   /* Sidebar (for non-clean theme) */
   --sidebar-bg: #d1d4d2;
 
+  /* Background photo tint — controls how much of the photo shows through */
+  --page-bg-tint: rgba(214, 214, 214, 0.85);
+
   /* Legacy CV content variables - theme-aware overrides */
   --text-dark: #1a1a1a;  /* Dark text for light background */
   --text-gray: #333333;  /* Secondary text for light background */
@@ -116,6 +119,9 @@
   /* Sidebar (for non-clean theme) - darker than light theme but lighter than main content */
   --sidebar-bg: #3a3d3e;
 
+  /* Background photo tint — darker overlay for dark theme */
+  --page-bg-tint: rgba(58, 58, 58, 0.85);
+
   /* Legacy CV content variables - theme-aware overrides */
   --text-dark: #e0e0e0;  /* Light text for dark background */
   --text-gray: #d0d0d0;  /* Secondary text for dark background */
@@ -171,6 +177,9 @@
     /* Sidebar (for non-clean theme) - matches explicit dark theme */
     --sidebar-bg: #3a3d3e;
 
+    /* Background photo tint — darker overlay for dark theme */
+    --page-bg-tint: rgba(58, 58, 58, 0.85);
+
     /* Legacy CV content variables - theme-aware overrides */
     --text-dark: #e0e0e0;  /* Light text for dark background */
     --text-gray: #d0d0d0;  /* Secondary text for dark background */

static/css/04-interactive/_buttons.css

@@ -124,6 +124,39 @@
     color: #27ae60; /* Green icon when at bottom */
 }
 
+/* Background Photo Toggle (Dev Only - above download button) */
+.bg-photo-btn {
+    position: fixed;
+    bottom: 30rem;
+    left: 2rem;
+    width: 50px;
+    height: 50px;
+    background: var(--black-bar, #2b2b2b);
+    color: white;
+    border: none;
+    border-radius: 50%;
+    cursor: pointer;
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.3);
+    transition: all 0.3s ease;
+    z-index: 999;
+    opacity: 0.6;
+}
+
+.bg-photo-btn:hover {
+    opacity: 1;
+    transform: translateY(-3px);
+    box-shadow: 0 6px 16px rgba(0, 0, 0, 0.4);
+    background: #8e6b3e !important; /* Earthy brown — Lanzarote vibes */
+}
+
+.bg-photo-btn.at-bottom {
+    opacity: 1;
+    background: #8e6b3e !important;
+}
+
 /* Download Button (TOP POSITION - now first button after cmd-k removed) */
 .download-btn {
     position: fixed;