feat: add baseline anti-cheat guards

[jianmosier]

Issue

Closes #2

Summary

• replaces the native client with buildable baseline anti-cheat guards for debugger detection and suspicious process detection
• keeps Windows native checks through IsDebuggerPresent, CheckRemoteDebuggerPresent, and ToolHelp process enumeration, with POSIX fallbacks so CI can compile and smoke-test the client
• adds a dependency-free Python monitor with the same debugger/process checks
• adds regression tests for suspicious-process matching, debugger detection, detection priority, and exit-code behavior
• documents exact run/test commands

Acceptance criteria

• Application exits when a debugger is detected.
• Application exits when a suspicious process is found.
• Works for both C++ client (AntiCheat.cpp) and Python monitor (anti_cheat.py).

Demo / verification

Native client smoke run:

[Javelin AntiCheat] starting checks...
[Javelin AntiCheat] All clear. Continue.

Python monitor smoke run:

[Javelin AntiCheat] All clear

Validation

• python3 -m unittest discover -s tests
• python3 -m py_compile anti_cheat.py tests/test_anti_cheat.py
• c++ -std=c++17 -Wall -Wextra -pedantic AntiCheat.cpp -o /tmp/javelin-anticheat-check
• /tmp/javelin-anticheat-check
• git diff --check

/claim #2