v0.1.6 — Desktop drag-and-drop + icon fix

Fixes file drag-and-drop into topic file panels (Subjects area) — Tauri was intercepting OS file drops at the WebView level, blocking the page's own drop handling. Also regenerates the desktop app icon set, which had gone stale after the web favicon was updated to the current dark-navy TW logo. (Supersedes v0.1.5, which shipped before the icon fix was caught.)