Fix icon loading for third-party apps with file:// URL scheme

- Add file:// URL handling to AssetFilesInterface in kernel.cpp
- Update home.lua to use file:// prefix for absolute filesystem paths
- Add file:// URL handling to desktop file interface for consistency

This fixes RmlUi stripping the leading slash from absolute paths
when resolving img src URLs relative to the document base.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/main/assets/apps/home/home.lua

@@ -121,9 +121,14 @@ function renderThirdPartyApps()
             else
                 icon_path = app.icon
             end
+            -- Use file:// prefix for absolute paths to prevent RmlUi URL resolution
+            local src_path = icon_path
+            if icon_path:sub(1, 1) == "/" then
+                src_path = "file://" .. icon_path
+            end
             -- Use img tag for actual icon
-            icon_html = '<img src="' .. icon_path .. '" style="width: 48px; height: 48px;"/>'
-            print("[Home] Loading icon: " .. icon_path)
+            icon_html = '<img src="' .. src_path .. '" style="width: 48px; height: 48px;"/>'
+            print("[Home] Loading icon: " .. src_path)
         else
             -- Fallback to initial letter
             icon_html = '<span style="font-size: 28px; color: #000000;">' .. initial .. '</span>'