chore(ci): adopt setup-vcpkg composite action

[kcenon]

What

Migrate messaging_system CI workflow from inline vcpkg setup logic to the reusable
composite action at kcenon/common_system/.github/actions/setup-vcpkg/.

Change Type

• Chore (CI/CD maintenance)

Affected Components

• .github/workflows/ci.yml — vcpkg setup steps in the build job

Why

Problem Solved

The inline vcpkg setup duplicates 54 lines of clone/bootstrap/cache logic that is
already encapsulated in the ecosystem composite action. This creates maintenance
burden — a bug fix in setup logic would require separate PRs in each repo.

Related Issues

• Part of chore(ci): adopt setup-vcpkg composite action across ecosystem CI workflows common_system#512 (adopt setup-vcpkg composite action across ecosystem)
• Composite action created in chore(ci): create reusable GitHub Actions composite action for ecosystem vcpkg setup common_system#511

Benefits

• Pins vcpkg to ecosystem baseline commit (previously cloned from HEAD)
• Standardizes cache key strategy across repos
• Reduces CI workflow from ~310 lines to ~260 lines
• Future vcpkg setup changes only need one PR (in common_system)

Where

Files Changed

File	Lines Changed	Type of Change
.github/workflows/ci.yml	+6 / -54	Replace inline vcpkg with composite action

Specific Changes

1. Removed 5 inline steps: Cache vcpkg, Setup Unix/Windows, Determine commit Unix/Windows
2. Added 1 composite action step: kcenon/common_system/.github/actions/setup-vcpkg@main
3. Updated vcpkg binary path to ${{ env.VCPKG_ROOT }}/vcpkg
4. Updated Windows CMake toolchain to ${{ env.CMAKE_TOOLCHAIN_FILE }}
5. Simplified vcpkg_installed cache key (removed dynamic commit hash)

How

Implementation Details

The composite action handles:

• Caching vcpkg directory with proper exclusions (buildtrees, packages, downloads)
• Cloning vcpkg pinned to ecosystem baseline commit d90a9b15
• Bootstrapping vcpkg (cross-platform)
• Setting VCPKG_ROOT and CMAKE_TOOLCHAIN_FILE environment variables

The build-without-network job is unchanged — it does not use vcpkg.

Test Plan

• CI passes on all 3 platforms (Ubuntu, macOS, Windows)
• vcpkg cache is restored correctly
• vcpkg_installed packages cache works
• Build and tests succeed as before

Breaking Changes

None — only CI infrastructure change, no source code modifications.