feat: add latency indicator and broadcast target selection

- Added a latency indicator to the status bar, displaying round-trip time for SSH sessions.
- Implemented functionality to select specific sessions for broadcasting input, allowing users to manage broadcast targets.
- Enhanced SFTP functionality with bookmark management, enabling users to bookmark directories and navigate to them easily.
- Introduced a modal for user-defined snippet variables, allowing dynamic command execution with placeholders.
- Added port forwarding management for SSH sessions, including the ability to start and stop port forwards.
- Improved terminal output export functionality, allowing users to download or copy terminal output to clipboard.

frontend/src/css/sftp.css

@@ -490,3 +490,25 @@
   font-size: 10px;
   color: var(--text-tertiary);
 }
+
+/* -----------------------------------------------------------------------
+   Bookmark list
+   ----------------------------------------------------------------------- */
+.sftp-bookmark-list {
+  max-height: 250px;
+  overflow-y: auto;
+}
+
+.sftp-bookmark-row {
+  display: flex;
+  align-items: center;
+  gap: var(--space-2);
+  padding: var(--space-1) var(--space-2);
+  border-radius: var(--radius-sm);
+  cursor: pointer;
+  transition: background var(--transition-fast);
+}
+
+.sftp-bookmark-row:hover {
+  background: var(--bg-hover);
+}