Implement SSH port forwarding and improve jump host UI

Port Forwarding (new):
- Add PortForward model with local/remote direction, bind/dest addresses
- Implement ForwardManager in sshclient/portforward.go with full
  bidirectional tunnel support for both local and remote forwarding
- Integrate ForwardManager into SSH client lifecycle (auto-start on
  connect, clean shutdown on close)
- Add session manager methods: ListPortForwards, StartPortForward,
  StopPortForward with event emission
- Add API surface: ListPortForwards, StartPortForward, StopPortForward
- Add validation for port-forward rules in ValidateSSHConfig
- Add port forwarding section to profile editor with direction, bind/dest
  host/port, label, and enable toggle
- Add frontend event handling for forward:started/stopped/error
- Style port-forward rows with charcoal card design matching jump hosts

Jump Host UI improvements:
- Add private key path field to jump host editor rows
- Collect privateKeyPath in form value collection
- Restyle jump host rows as two-line cards with clear field grouping

frontend/src/js/app.js

@@ -180,6 +180,21 @@ class App {
             );
         });
 
+        // Port-forwarding events
+        window.runtime.EventsOn('session:forward:started', (payload) => {
+            const fwd = payload.forward || {};
+            const label = fwd.label || `${fwd.bindHost || ''}:${fwd.bindPort} → ${fwd.destHost}:${fwd.destPort}`;
+            this.notifications.success(`Forward started: ${label}`);
+        });
+
+        window.runtime.EventsOn('session:forward:stopped', (payload) => {
+            this.notifications.info(`Forward stopped: ${payload.forwardID}`);
+        });
+
+        window.runtime.EventsOn('session:forward:error', (payload) => {
+            this.notifications.error(`Forward error: ${payload.error}`);
+        });
+
         // Telnet negotiation debug messages
         window.runtime.EventsOn('session:debug', (payload) => {
             console.debug('[session:debug]', payload);