[FEATURE]: Session list panel in sidebar showing active sessions and pending approvals #22315

Feature hasn't been suggested before.

• I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

Problem:
The current TUI sidebar only displays status information for the active session (session title, Context, MCP, LSP). There is no way to see all running sessions or sessions waiting for approval without navigating away from the current view (/sessions or <leader>l).

When running multiple sessions in parallel (e.g., several Task agents or long-running operations), it's difficult to know which sessions need attention (pending approval) without manually cycling through them.

Proposed Solution:
Add an optional session list panel to the sidebar that shows:

1. All active sessions with a brief status indicator (running, idle, waiting)
2. Sessions pending approval highlighted or grouped separately so they're immediately visible
3. Ability to click/select a session from the list to switch to it

This could be:

• A new section in the existing sidebar (below the current status info)
• A configurable sidebar mode (toggle between "status view" and "session list view")
• A tui.json option like "sidebar_mode": "sessions" or "sidebar_sections": ["status", "sessions"]

Current Workaround:

• Use /sessions command or <leader>l keybind to open the session list view
• Use session navigation keybinds (<leader>down, right/left, up) to cycle through sessions
• Use opencode sessions CLI command

These work but require leaving the current context, which breaks flow -- especially when monitoring multiple concurrent agents.

Why This Matters:
As OpenCode's agent capabilities grow (Task tool, parallel agents, long-running operations), users increasingly run multiple sessions simultaneously. Having at-a-glance visibility into which sessions need attention (especially approval gates) would significantly improve the multi-session workflow.