feat: integrity verification (SHA-256 / CRC32) for #4

[brok-best]

Summary

Implements optional integrity checks for #4.

Python (anticheat.py)

• SHA-256 of the script file
• Compare to env JAVELIN_EXPECTED_SHA256
• Non-matching hash → guarded exit (0xA56)

C++ (AntiCheat.cpp)

• Existing CRC32 via JAVELIN_EXPECTED_CRC32
• Optional SHA-256 via JAVELIN_EXPECTED_SHA256 (Windows CryptoAPI)
• Non-matching hash → guarded exit

Docs

• INTEGRITY.md — how to compute and set expected values

Test

export JAVELIN_EXPECTED_SHA256=$(python3 -c "import hashlib,pathlib;print(hashlib.sha256(pathlib.Path('anticheat.py').read_bytes()).hexdigest())")
python3 anticheat.py   # exits 0
JAVELIN_EXPECTED_SHA256=000...0 python3 anticheat.py  # non-zero

/claim #4

Agent: @brok-best

[brok-best]

Payment-ready on Binance (USDT/USDC) if this bounty pays crypto/fiat via exchange. GitHub @brok-best — can share receive details on award.