footer : fix show/hide logic, transition and scroll throttle. related to #51

- Fix scroll listener (cleanup, local querySelector, scrollHeight calc)
- Fix media query syntax in variables.css (missing space in `and (`)
- Use transform: translateY instead of bottom for GPU-accelerated transition
- Throttle scroll handler with requestAnimationFrame
- Move Footer to App.svelte (global), remove per-view imports

refs #51

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

src/views/About.svelte

@@ -4,7 +4,6 @@
   import { navigation } from '@state/navigation.svelte'
 
   import { t } from '@i18n'
-  import Footer from '@components/layout/Footer.svelte'
 
   let { data } = $props()
 
@@ -168,8 +167,6 @@
         </div>
       </section>
     {/if}
-
-    <Footer />
   </div>
 </div>
 

src/views/Article.svelte

@@ -6,7 +6,6 @@
 
   import { t } from '@i18n'
   import { onMount } from 'svelte'
-  import Footer from '@components/layout/Footer.svelte'
   import WhitePaperDialog from '@components/WhitePaperDialog.svelte'
   import ShareButtons from '@components/blocks/ShareButtons.svelte'
   import ArticleRelated from '@components/blocks/ArticleRelated.svelte'
@@ -144,8 +143,6 @@
     <ArticleRelated related={data.related} />
   {/if}
 </article>
-
-<Footer />
 </div>
 
 <WhitePaperDialog uri={activeWhitePaperUri} onClose={() => activeWhitePaperUri = null} />

src/views/Blog.svelte

@@ -5,7 +5,6 @@
 
   import Article from '@views/Article.svelte'
   import { t } from '@i18n'
-  import Footer from '@components/layout/Footer.svelte'
 
   let { data } = $props()
 
@@ -183,8 +182,6 @@
       {#if articleLoading}
         <p class="collection-loading">{t('loading')}</p>
       {/if}
-
-      <Footer />
     </div>
 
   {/if}

src/views/Privacy.svelte

@@ -1,6 +1,5 @@
 <script>
   import { navigation } from '@state/navigation.svelte'
-  import Footer from '@components/layout/Footer.svelte'
 
   let { data } = $props()
 
@@ -28,8 +27,6 @@
         {/each}
       </section>
     {/if}
-
-    <Footer />
   </div>
 </div>
 

src/views/WhitePapers.svelte

@@ -4,7 +4,6 @@
   import { locale } from '@state/locale.svelte'
   import WhitePaper from '@views/WhitePaper.svelte'
   import { t } from '@i18n'
-  import Footer from '@components/layout/Footer.svelte'
 
   let { data } = $props()
 
@@ -154,8 +153,6 @@
       {#if itemLoading}
         <p class="collection-loading">{t('loading')}</p>
       {/if}
-
-      <Footer class="page-scrollable-footer" />
     </div>
   {/if}
 </section>