fix(filter): don't drop memory-safety findings in .hpp/.cxx/.hh C++ files

[vidigoat]

Problem

HardExclusionRules.get_exclusion_reason (claudecode/findings_filter.py) excludes memory-safety findings as "not applicable" for any file whose extension is not in this set:

c_cpp_extensions = {'.c', '.cc', '.cpp', '.h'}

That set omits the common C++ extensions .hpp, .hh, .cxx, .hxx, .c++, .h++ and template-implementation extensions (.ipp, .tpp, .inl). .hpp is the dominant C++ header extension, and because headers hold inline functions and templates, they are exactly where memory-safety bugs (buffer overflow, use-after-free, OOB) tend to live. So genuine memory-safety findings in real C++ files were being silently dropped before they could be reported.

This contradicts the documented intent of the existing test test_memory_safety_not_excluded_cpp_files ("memory safety issues are NOT excluded in C/C++ files").

Reproduction

get_exclusion_reason on a buffer-overflow finding in object.hpp or a use-after-free in engine.cxx returns "Memory safety finding in non-C/C++ code (not applicable)" instead of None (keep). On main the new test fails for exactly these cases.

Fix

Extend c_cpp_extensions to include the standard C++ header/source and template-impl extensions.

Tests

Added test_memory_safety_not_excluded_cpp_header_and_alt_extensions covering .hpp, .cxx, .hh, .hxx, .ipp. It fails on main and passes with the fix; the full claudecode suite (174 tests) stays green, including the existing case-insensitive and non-C/C++ exclusion tests (a .py memory-safety finding is still correctly excluded).

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Authored with AI assistance (Claude); bug reproduced, fix written, and the full test suite verified locally before submitting.