revert(firefox): use new-tab-override instead of tridactyl dynamic newtab

Tridactyl dynamic environment variables proved unreliable. Reverting to the verified extension-based solution.

apps/firefox/default.nix

@@ -16,7 +16,7 @@
     ];
 
     workspace = [
-      "special:youtube, on-created-empty:env TRIDACTYL_NEWTAB=https://youtube.com firefox -P YouTube --name youtube"
+      "special:youtube, on-created-empty:uwsm app -- firefox -P YouTube --name youtube"
     ];
 
     windowrulev2 = [
@@ -38,10 +38,6 @@
     bind J tabnext
     bind K tabprev
     unbind <C-e>
-
-    " Modular NewTab: Set from environment variable if provided by launch command
-    " Note: Uses 'r.content' for native command output
-    js tri.native.run("sh -c 'echo $TRIDACTYL_NEWTAB'").then(r => { let url = r.content.trim(); if (url) { tri.config.set("newtab", url); console.log("Tridactyl: Set newtab to " + url); } }).catch(e => console.error("Tridactyl NewTab Env Error:", e))
   '';
 
   programs.firefox = {