drift doctor + hivemind patch-level in the startup banner

[ApexDevelopment]

Half of a recent homelab debugging session was environment forensics that a drift doctor command could do in seconds:

• Is the installed hivemind wheel current? A desktop was running a wheel predating the per-thread replicate_p2p fix from scripts/hivemind-win32.patch; every server start deadlocked in handler registration. There was no way to tell short of grepping site-packages. Suggest: build_hivemind_windows.py stamps a patch revision into the wheel, the server logs it in the startup banner, and doctor compares it against the in-repo patch.
• Stray processes: orphaned p2pd.exe daemons (see Tie p2pd child lifetime to the server process #5) and leftover run_server pythons squatting ports.
• GPU sanity: a 5-second SDPA numeric check (GPU vs CPU max-diff at a few head_dims/dtypes) to rule out backend kernel bugs early on ROCm/MPS/XPU.
• Torch/device/dtype summary.

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