Add security hardening compiler flags for local development builds

[Plenvorik]

Summary

Add compiler security hardening flags to CMakeLists.txt for local development builds. While Fedora's RPM build system automatically adds these flags via %cmake macro, explicitly setting them ensures consistent security posture across all build environments.

Current State

set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} -O2 -DNDEBUG")

Proposed Addition

# Security hardening flags
set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} -O2 -DNDEBUG -D_FORTIFY_SOURCE=2 -fstack-protector-strong")
set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} -Wl,-z,relro,-z,now")

Flags Explained

Flag	Purpose
-fstack-protector-strong	Detects stack buffer overflows
-D_FORTIFY_SOURCE=2	Runtime buffer overflow detection
-Wl,-z,relro,-z,now	Full RELRO - protects GOT from overwrites

Priority

Low - This is a defense-in-depth improvement. RPM builds via rpmbuild or fedpkg already include these flags automatically.