Support background tool execution

Background\nTool execution (e.g., bash/task/batch) waits for child processes to exit and cannot keep running in the background; only service processes like LSP are long‑lived.\n\n## Expected\nSupport tools running persistently in the background (e.g., long‑running tasks/daemons), with the ability to check status, view output, and stop them.\n\n## Possible direction\n- Add tool execution modes: foreground / background\n- Provide status and log query APIs for background jobs\n- Provide explicit stop/cleanup mechanisms

This issue might be a duplicate of existing issues. Please check:

[feat] True Async/Background Sub-Agent Delegation #5887: [feat] True Async/Background Sub-Agent Delegation - requests non-blocking async sub-agent execution
feat: Show background tasks status in sidebar #8322: feat: Show background tasks status in sidebar - addresses visibility for background tasks
[FEATURE]: Better active/background terminal and bash management #6375: [FEATURE]: Better active/background terminal and bash management - proposes background terminal suite with query APIs
Feature Request: Add Background Bash Execution (Like Claude Code’s Ctrl+b) #1970: Feature Request: Add Background Bash Execution - requests background bash execution similar to Claude Code's Ctrl+b

Feel free to ignore if none of these address your specific case.