Add rbw SSH socket support in home-manager modules

- Introduced a new module `rbw-ssh-socket.nix` to manage SSH_AUTH_SOCK for rbw.
- Updated `default.nix` to utilize the new SSH socket variable for session management.
- Refactored Bash and Fish shell configurations to use the new module for setting SSH_AUTH_SOCK, improving maintainability and consistency across shell environments.

modules/ssh/home-manager/default.nix

@@ -56,14 +56,14 @@
       }
       {
         home.packages = with pkgs; [ rbw pinentry-gtk2 ];
-        home.sessionVariables.SSH_AUTH_SOCK = "$XDG_RUNTIME_DIR/rbw/ssh-agent-socket";
+        home.sessionVariables.SSH_AUTH_SOCK = self.lib.rbwSshSocket.sessionVariable;
         home.file = inventory.mkIdentityFiles selectedHosts;
 
         programs.ssh.enable = lib.mkIf cfg.manageSshConfig false;
         home.activation.rbwSshConfig = lib.mkIf cfg.manageSshConfig (lib.hm.dag.entryAfter [ "writeBoundary" ] ''
           mkdir -p "$HOME/.ssh"
           chmod 700 "$HOME/.ssh"
-          RBW_SSH_SOCK="/run/user/$(id -u)/rbw/ssh-agent-socket"
+          RBW_SSH_SOCK="${self.lib.rbwSshSocket.activationPath}"
           cat > "$HOME/.ssh/config" <<'EOF'
 ${sshConfigTemplate}
 EOF