Fix Windows privacy writes and duplicate PR CI

[HLLMR]

Summary

• retry only classified Windows replacement-contention failures within a bounded two-second window
• make the Windows contention test publish its synchronization signal atomically and reap helper processes deterministically
• preserve privacy-screen locking, atomic replacement, link protection, and nondisclosing failures
• retain the complete native OS and Python 3.10-3.14 pull-request matrix
• reconcile current documentation and public governance with accepted WO-WW-017 and WO-WW-018

Verification

• two independent 136-file public projections are byte-identical; complete-tree ledger SHA-256: 9dee62041cadbf44cd34eda0a409891b5cf78e85796e77c26845866bc8fef1d6
• retained Windows candidate: 753 tests passed, 2 documented skips
• final projection checker passed on both retained candidates
• fresh restricted Sonnet publication review: ACCEPT, high confidence, no blocking findings

Closes #18
Closes #19
Closes #27