[FEATURE]: keep a history of TUI toast notifications

Feature request: keep a history of TUI toast notifications

Problem

Toasts in the TUI are single-slot: a new toast replaces the previous one, and they disappear after about 5 seconds. There is no way to review a notification once it is gone. During long agent runs, provider errors, rate limits, MCP alerts and plugin failures are frequently missed.

Proposal

Keep a bounded notification history and make it reviewable (e.g. a dialog plus keybind) with timestamp, variant and full message. Persisting the same entries to a log file would be a nice bonus.

Notes

• tui.toast.show and session.error are already published on the server event bus, so a server plugin can capture those as a workaround — I published a small one here: https://github.com/LouisLau-art/opencode-toast-history
• However, toasts that the TUI renders locally (without a corresponding server event) are not observable from plugins, so full coverage needs a core change. That is why I am filing this.
• Happy to help if you can point at where this should live (the toast store already keeps the current toast; a small ring buffer would probably be enough).

Start by tracing the TUI toast store and the tui.toast.show and session.error events on the server event bus, including locally rendered toasts. Define a bounded history that can be reviewed through a dialog and keybind, showing each notification's timestamp, variant, and full message; verify that older entries are evicted and notifications remain reviewable after dismissal.