Windows native support (named pipe + psmux)

[shobgj132]

Summary

• CCB Windows native support without WSL dependency
• Named Pipe IPC replacing Unix socket on Windows
• psmux backend replacing tmux on Windows
• 25+ fixes covering the full stack: process spawn, pipe communication, session lifecycle, keeper stability

Key changes

• Windows detached process spawn (CREATE_NEW_PROCESS_GROUP + DETACHED_PROCESS + CREATE_NO_WINDOW)
• Named Pipe multi-instance with spare handle pre-creation
• Named Pipe readiness probe retry loop
• Windows PID liveness check via tasklist (replacing os.kill)
• Keeper restart storm protection (max 5 retries)
• JSON store read locking for Windows file contention
• Skip self pipe probe in daemon health/startup report
• psmux placeholder using cmd.exe instead of pwsh (session stability)
• Skip WSL-dependent tmux UI scripts on Windows/psmux
• Extended probe/heartbeat timeouts for Windows
• Hardened system tool paths (absolute paths to prevent PATH hijacking)
• Global subprocess CREATE_NO_WINDOW monkey-patch to prevent console popups

Test plan

• V1: Installation verification (ccb --version)
• V2: Daemon startup (named_pipe + psmux, status=ok)
• V3: Agent communication (ccb ask)
• V4: Task dispatch and retrieval (ccb pend)
• All changes gated by os.name == 'nt', Linux/macOS unaffected

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