footer : fix data-template sync and atBottom overflow guard refs #59

- App.svelte: sync body[data-template] on every active template change.
  PHP only sets it on initial load; SPA navigation left it stale (e.g.
  stuck on "home"), breaking CSS selectors like [data-template="white-paper"].
- Footer.svelte: guard atBottom with an overflow check.
  When scrollHeight === clientHeight (no overflow), the old formula
  (0 >= 0 - threshold) was always true, showing the footer immediately
  on pages with no scrollable content (e.g. white-paper detail on load).

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

@@ -23,8 +23,14 @@
     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
       })