Update flake.lock and vscode configuration

- Updated package references in flake.lock for various dependencies.
- Changed VSCode package from vscodium to vscode and updated extensions.
- Enabled SSH agent start in ssh.nix.
- Refined overlays in default.nix for better package management.

hosts/common/core/ssh.nix

@@ -4,7 +4,7 @@
   ...
 }: {
   programs.ssh = lib.optionalAttrs pkgs.stdenv.isLinux {
-    startAgent = false;
+    startAgent = true;
     enableAskPassword = true;
   };
 }