Key-file picker in the connection manager

Choose... button beside the private-key field opens the native file dialog
starting in ~/.ssh (Utils.openFileDialog via a pickKeyFile RPC).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

ui/src/app/connection-manager/connection-manager.html

@@ -196,13 +196,22 @@
             } @else {
               <label class="flex flex-col gap-1 text-xs">
                 <span class="text-muted-foreground">Private key file</span>
-                <input
-                  [value]="d.privateKeyPath"
-                  (input)="patch('privateKeyPath', $any($event.target).value)"
-                  placeholder="~/.ssh/id_ed25519"
-                  spellcheck="false"
-                  class="h-7 rounded-md border border-input bg-transparent px-2 font-mono outline-none focus:ring-2 focus:ring-ring"
-                />
+                <div class="flex items-center gap-1">
+                  <input
+                    [value]="d.privateKeyPath"
+                    (input)="patch('privateKeyPath', $any($event.target).value)"
+                    placeholder="~/.ssh/id_ed25519"
+                    spellcheck="false"
+                    class="h-7 min-w-0 flex-1 rounded-md border border-input bg-transparent px-2 font-mono outline-none focus:ring-2 focus:ring-ring"
+                  />
+                  <button
+                    type="button"
+                    (click)="pickKeyFile()"
+                    class="h-7 shrink-0 rounded-md border border-border px-2 text-[11px] hover:bg-accent"
+                  >
+                    Choose…
+                  </button>
+                </div>
               </label>
               <label class="flex flex-col gap-1 text-xs">
                 <span class="text-muted-foreground">Passphrase (optional)</span>