footer : remove immediate onScroll call on slide change refs #59

Calling onScroll() immediately after attaching the listener caused the
footer to appear on page load when content height exceeded clientHeight
by less than the threshold (0 >= smallOverflow - 100 = true at scrollTop=0).
Footer now starts hidden and only reveals on explicit user scroll.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/App.svelte

@@ -64,6 +64,12 @@
     img.src = BG_URL
   }
 
+  // Sync body[data-template] with the active template so CSS selectors (e.g. footer hide)
+  // stay correct on SPA navigation — PHP only sets it on the initial page load.
+  $effect(() => {
+    if (activeTemplate) document.body.dataset.template = activeTemplate
+  })
+
   // Active la transition seulement après le premier paint à la bonne position.
   // Double rAF : le premier laisse passer un paint avec le bon translateX,
   // le second active is-animated — évite l'animation parasite au chargement.

src/components/layout/Footer.svelte

@@ -23,15 +23,23 @@
     function onScroll() {
       if (rafId) return
       rafId = requestAnimationFrame(() => {
-        const threshold = window.innerWidth > 800 ? 100 : 200
-        const atBottom = scrollableContainer.scrollTop >= scrollableContainer.scrollHeight - scrollableContainer.clientHeight - threshold
+        const scrollHeight  = scrollableContainer.scrollHeight
+        const clientHeight  = scrollableContainer.clientHeight
+        const threshold     = window.innerWidth > 800 ? 100 : 200
+        // Only show footer when content actually overflows AND user is near the bottom.
+        // Without the overflow guard, atBottom is true even when scrollHeight === clientHeight
+        // (0 >= 0 - threshold), causing the footer to appear on pages with no scroll.
+        const overflows = scrollHeight > clientHeight
+        const atBottom  = overflows && scrollableContainer.scrollTop >= scrollHeight - clientHeight - threshold
         isHidden = !atBottom
         rafId = null
       })
     }
 
     scrollableContainer.addEventListener('scroll', onScroll)
-    onScroll()
+    // No immediate onScroll() call: footer starts hidden and only reveals when
+    // the user actively scrolls near the bottom. Calling it immediately caused
+    // the footer to flash on page load when content barely exceeded the threshold.
 
     return () => {
       scrollableContainer.removeEventListener('scroll', onScroll)