Add async tasks support documentation

[jancurn]

Summary

This PR updates the README documentation to reflect support for MCP async tasks, a feature that allows tools to run as background tasks with progress tracking and lifecycle management.

Changes

• Feature announcement: Updated the feature list to include "async tasks" alongside existing MCP support capabilities
• Feature documentation: Added comprehensive "Async tasks" section with:
  • Usage examples for --task flag (waits for completion with progress spinner)
  • Usage examples for --detach flag (starts task and returns immediately)
  • Task management commands (tasks-list, tasks-get, tasks-cancel)
  • Details about progress tracking, ESC key handling, and task annotations
• Feature matrix:
  • Added "Tasks" column to the MCP client comparison table
  • Updated star counts and tool ordering to reflect current GitHub metrics
  • Updated legend to document async tasks support
  • Marked mcpc as supporting async tasks (✅)

Implementation Details

The documentation now clearly explains the full async task lifecycle:

• Starting tasks with progress monitoring (--task)
• Detached task execution (--detach)
• Task status checking and cancellation
• Tool-level task support annotations ([task:optional], [task:required], [task:forbidden])

This aligns mcpc's documentation with the MCP specification for async tasks.

https://claude.ai/code/session_01182EJocDGYXNrXYvCbWRaV