fix(mime): text/plain falls through to Text Editor on live (#119)

A singleton default naming code.desktop left the live ISO with no text
handler — GIO skips missing .desktop files and offers nothing. Prefer
vscode when present, then org.gnome.TextEditor.desktop. Live also gains
mpv (video defaults had the same hole; free via the template pin).

checks.live-baseline-apps now requires every Default Applications key
to resolve to a present .desktop on live (HM + system path) and on the
default template install. Proved to fail on a vscode-only text/plain.

Verified: V2 (live-baseline-apps green + prove-to-fail); V0 flake check.

modules/home/mime.nix

@@ -44,8 +44,12 @@ lib.mkIf config.nomarchy.mime.enable {
       "audio/x-m4a" = "io.bassi.Amberol.desktop";
       "audio/aac" = "io.bassi.Amberol.desktop";
 
-      # The template's active editor; degrades if you drop vscode.
-      "text/plain" = "code.desktop";
+      # Prefer the template's vscode; fall through to gnome-text-editor
+      # (ships on the live ISO after #103, and is the only editor there).
+      # A singleton that names an absent .desktop is silently skipped by
+      # GIO and leaves no handler at all — the #94 / #119 trap. HM tries
+      # the next entry when the preferred one is missing.
+      "text/plain" = [ "code.desktop" "org.gnome.TextEditor.desktop" ];
 
       # The system-side Thunar (nomarchy.system.fileManager).
       "inode/directory" = "thunar.desktop";