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/layout.css

@@ -169,6 +169,20 @@
   background: var(--text-tertiary);
 }
 
+/* Latency indicator */
+#status-latency {
+  font-variant-numeric: tabular-nums;
+}
+#status-latency.latency-good {
+  color: var(--success);
+}
+#status-latency.latency-warn {
+  color: var(--warning);
+}
+#status-latency.latency-bad {
+  color: var(--error);
+}
+
 /* -----------------------------------------------------------------------
    Resize handle (between sidebar and workspace)
    ----------------------------------------------------------------------- */