Add bash mode for executing shell commands

- Add ! prefix in TUI editor to execute shell commands directly
- Output streams in real-time and is added to LLM context
- Supports multiline commands, cancellation (Escape), truncation
- Preview mode shows last 20 lines, Ctrl+O expands full output
- Commands persist in session history as bashExecution messages
- Add bash command to RPC mode via {type:'bash',command:'...'}
- Add RPC tests for bash command execution and context inclusion
- Update docs: rpc.md, session.md, README.md, CHANGELOG.md

Closes #112

Co-authored-by: Markus Ylisiurunen <markus.ylisiurunen@gmail.com>

packages/coding-agent/CHANGELOG.md

@@ -14,6 +14,8 @@
 
 - **Collapse changelog setting**: Add `"collapseChangelog": true` to `~/.pi/agent/settings.json` to show a condensed "Updated to vX.Y.Z" message instead of the full changelog after updates. Use `/changelog` to view the full changelog. ([#148](https://github.com/badlogic/pi-mono/issues/148))
 
+- **Bash mode**: Execute shell commands directly from the editor by prefixing with `!` (e.g., `!ls -la`). Output streams in real-time, is added to the LLM context, and persists in session history. Supports multiline commands, cancellation (Escape), truncation for large outputs, and preview/expand toggle (Ctrl+O). Also available in RPC mode via `{"type":"bash","command":"..."}`. ([#112](https://github.com/badlogic/pi-mono/pull/112), original implementation by [@markusylisiurunen](https://github.com/markusylisiurunen))
+
 ## [0.13.2] - 2025-12-07
 
 ### Changed