chore(foundation): harden build and core invariants

[czlin7]

Summary

• replace machine-specific Visual Studio/SFML project assumptions with a portable CMake build;
• use an installed SFML 3.1 package when available, otherwise fetch SFML 3.1.0 with only the modules EcoSimEngine needs;
• normalize case-sensitive include/source paths and fix strict-compiler header dependencies;
• copy config/ and resources/ next to the application after build;
• remove stale generated/project residue and tracked ImGui runtime state;
• harden ComponentManager and SystemManager invariant handling;
• fix Action::toString() enum/string drift and remove its unsafe formatting assumptions;
• add dependency-free CTest coverage for component storage, system membership, and EventBus behavior;
• add CI coverage for headless foundation tests plus complete Linux and Windows application builds;
• refresh README/build documentation to match the repository's current state.

Validation

GitHub Actions run 32844161695 passes all merge gates:

• foundation-tests — configure, build, and CTest: passed;
• linux-app-build — clean Ubuntu 22.04 configure and full application build/link: passed;
• windows-app-build — clean Windows/MSVC configure and full Release application build/link: passed.

The headless foundation suite also passes independently with the application/SFML path disabled.

Scope

This PR intentionally does not add simulation features or redesign the ECS. It establishes a reproducible cross-platform build/test baseline and fixes correctness issues exposed while validating that baseline.

Interactive GUI launch behavior is not exercised by CI; the desktop application is nevertheless compiled and linked successfully on both Linux and Windows, including the post-build runtime resource copy step.