branding: add EverShelf logo to kiosk splash + web header/preloader

- assets/img/logo/logo.png: trimmed full logo (icon + text, transparent bg)
- assets/img/logo/logo_icon.png: icon-only crop (no text, for header)
- drawable-*/ic_logo.png: multi-density PNGs for Android splash (mdpi→xxxhdpi)
- activity_kiosk.xml: replace ic_launcher_foreground with ic_logo at 260dp,
  remove redundant 'EverShelf' text row (already in logo image)
- index.html: add logo_icon.png in header title, logo.png in preloader
- style.css: add .app-preloader-logo and .header-logo-icon rules

index.html

@@ -54,7 +54,7 @@
 <div id="app-preloader" aria-hidden="true">
     <div class="app-preloader-inner">
         <div class="app-preloader-spinner"></div>
-        <span class="app-preloader-label">🏠 EverShelf</span>
+        <img src="assets/img/logo/logo.png" alt="EverShelf" class="app-preloader-logo" />
     </div>
 </div>
 
@@ -67,7 +67,7 @@
         <!-- Title — left-aligned; grows to fill space -->
         <div class="header-title-wrap">
             <h1 class="header-title" onclick="showPage('dashboard')">
-                <span data-i18n="nav.title">🏠 EverShelf</span><span class="header-version">v1.7.1</span>
+                <img src="assets/img/logo/logo_icon.png" alt="" class="header-logo-icon" aria-hidden="true" /><span data-i18n="nav.title">EverShelf</span><span class="header-version">v1.7.1</span>
             </h1>
             <!-- Update badge — shown alongside title, never replaces it -->
             <span class="header-update-badge" id="header-update-badge" style="display:none"></span>