[FEATURE]: Collapsible tool output (code/diff/blocks) in TUI

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

Tool output blocks (Write, Edit, Shell, GenericTool) render fully expanded, adding noise in long sessions and making chain-of-thought hard to follow.

Request: Add a global toggle (/collapse slash command + optional keybind) that collapses all tool blocks to a summary line (file name / diff stats / line count). Per-block click-to-expand via local override on top of the global mode.

Working prototype on my fork: https://github.com/aravasio/opencode/tree/collapse-tool-output

Happy to open a PR if this direction is accepted.

Screenshots for reference