[FEATURE] Option to show all sessions in the session list without repeated 'Load more'

Describe the enhancement you want to request

The session list in the sidebar (TUI, desktop app and web) is paginated: to reach older sessions you have to click "Load More" multiple times. With many sessions this is tedious, and there is no way to display the whole list at once.

I checked the current TUI docs and the live schema at https://opencode.ai/tui.json: there is no option like session_list_limit (or equivalent) to control this.

Proposed behavior

Add a configurable setting in tui.json, e.g. session_list_limit, that accepts a positive integer or "none" (show all sessions). This would avoid the repeated "Load More" clicks for users with hundreds of sessions.

Current workarounds

• /sessions (ctrl+x then l) opens the searchable session picker to jump to any session.

Additional context

• Related earlier proposal: https://github.com/anomalyco/opencode/issues/20754 (PR #6138)