chore/fix-icon-zim: fix logo and text cloud saturation

[luisguzman-adfa]

Fix welcome page logo, wordmark, tagline, and label layout

• Use the correct head-and-brain vector (from splash_logo.xml)
• Drop the "K2Go" wordmark that overlapped the logo; branding now lives in the footer ("Knowledge To Go").
• Move the tagline just below the emblem (JS-positioned under the outer ring), clear of the on-screen navigation bar.
• Place language labels by width: long names go top/bottom where there is room, short ones to the sides — this declutters the top-left corner automatically, with no manual repositioning.