feat(firefox): generalize youtube profile into modular web-app profile

- Renamed profiles/youtube.nix to profiles/web-app.nix.

- Refactored to accept id, name, and url as arguments.

- Added settings to force homepage on startup and new tabs.

- Disabled session restore and undo-close-tab for web-app profiles.

apps/firefox/default.nix

@@ -49,7 +49,12 @@
     ];
 
     profiles = {
-      youtube = import ./profiles/youtube.nix {inherit pkgs myConfig;};
+      youtube = import ./profiles/web-app.nix {
+        inherit pkgs myConfig;
+        id = 1;
+        name = "YouTube";
+        url = "https://youtube.com";
+      };
       hakase = {
         search.force = true;
         isDefault = true;