fix(cmake): update install rules for migrated header paths

[kcenon]

Summary

• Add missing include/container/ forwarding headers to cmake install rules (for #include <container/...> paths)
• Add missing messaging/ directory to cmake install rules (message_container.h)

Why

PR #440 migrated headers from core/ to include/kcenon/container/, but the cmake install rules were not fully updated. When network_system CI runs cmake --install on container_system, the new forwarding headers under include/container/ and the messaging/ directory headers are not installed, causing downstream build failures on Windows MSVC (and potentially other platforms).

Relates to network_system PRs #864, #865, #866 which fail on Windows due to this.

Where

• CMakeLists.txt (install rules section, lines ~588-620)

How

Changes

1. Added install rule for include/container/ directory (forwarding headers that bridge #include <container/optimizations/fast_parser.h> to the canonical include/kcenon/container/ location)
2. Added messaging/ to the existing backward-compatible install rule (alongside core/, internal/, integration/)
3. Updated the install section documentation comment to reflect all installed directories

Verification

• Built successfully: cmake --build build
• Installed to temp prefix: cmake --install build --prefix /tmp/container_install_test
• Confirmed all headers are present in the install tree:
  • include/kcenon/container/ (canonical headers)
  • include/container/optimizations/fast_parser.h (forwarding header, previously missing)
  • include/messaging/message_container.h (previously missing)
  • include/core/, include/internal/, include/integration/ (unchanged)

Test plan

• CI passes on all platforms (Linux, macOS, Windows MSVC)
• Verify network_system CI can find container_system headers after this fix

[github-actions]

Performance Benchmark Report

Summary

• Total benchmarks: 0
• Regressions: 0 ✅
• Improvements: 0
• Unchanged: 0 (within 10% threshold)

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✅ Status: No significant performance regressions detected.