agent-host: Pause SSH reconnect after auth cancellation (#316810)

* agent-host: Pause SSH reconnect after auth cancellation (Written by Copilot)

When startup restore hits a keyboard-interactive prompt and the user cancels it, treat the cancellation as an intentional pause instead of a retryable reconnect failure. This avoids repeatedly reopening the password prompt during auto-reconnect. (Written by Copilot)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* agent-host: Reconnect SSH hosts on demand (Written by Copilot)

Route host-picker reconnect and disconnect actions for stored SSH hosts through the SSH service. This lets a user manually reconnect after canceling startup auto-reconnect without deleting the stored host or hitting the generic WebSocket reconnect no-op. (Written by Copilot)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* agent-host: Handle all manual SSH reconnects (Written by Copilot)

Route manual reconnects for stored SSH hosts through the SSH service even when the entry does not have an SSH config alias, and disconnect using the SSH connection key so the host picker can cancel or reconnect the right connection. (Written by Copilot)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

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Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>