fix: batch fixes for issues #2782, 2783, 2784, 2785, 2786, 2788, 2789, 2791, 2792 (#368)

#2782: Ctrl+W now correctly deletes word backward in TUI input
#2783: Insert key is now handled (placeholder for future overwrite mode)
#2784: Double-click now selects word at cursor in input field
#2785: Terminal state is properly saved/restored on Ctrl+Z suspend/resume
#2786: Windows console now enables VT processing for ANSI sequences
#2788: Improved async task cancellation with proper HTTP connection cleanup
#2789: Added graceful shutdown for WebSocket/HTTP sessions on server exit
#2791: MCP child processes now have filtered environment (no secrets)
#2792: TUI streaming output optimized with dirty tracking, reduced idle FPS

[skip ci]

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Co-authored-by: Droid Agent <droid@factory.ai>

Author: 3 people