Summary

Extract pacs_system's modular cmake/*.cmake decomposition into a reusable kcenon-cmake-template/ so the other 7 systems can adopt it as a drop-in. Today only pacs_system follows this pattern; the other 7 carry monolithic root CMakeLists.txt files (range 150-1032 lines).

Part of #656. Depends on the layout standard from #658.

Why

• pacs_system already proves the modular pattern works in production
• Extracting once and reusing saves the same decomposition work in 7 systems
• A versioned template makes upgrades coordinated rather than ad-hoc

Scope

1. Identify the 8 canonical modules in pacs_system: options.cmake, compiler.cmake, dependencies.cmake, targets.cmake, install.cmake, testing.cmake, examples.cmake, warnings.cmake
2. Generalize each module to remove pacs-specific assumptions (project name, namespace, target list)
3. Place the template under cmake/template/ (or as a separate directory-scoped artifact) with a README explaining adoption steps
4. Document the template version and how downstream systems track upgrades

Acceptance Criteria

• All 8 cmake modules extracted into the template location
• Each module has a header comment naming its responsibility and required input variables
• Template README describes: directory layout, required variables, adoption checklist, version policy
• common_system itself adopts the template (replacing existing root CMakeLists.txt fallbacks)
• Existing common_system build/tests still pass after adoption

Out of Scope

• Migrating other 7 systems (handled by their respective sub-EPICs in [EPIC] Ecosystem-wide directory structure standardization #657)
• Cross-build CI workflow (ci(infra): add ecosystem cross-build workflow #660)