DEFECT: CMAKE CI test obsolete after artifact cleanup blocks all PRs

[krystophny]

Issue Description

The CMAKE CI test in .github/workflows/ci.yml lines 97-115 fails because it references the root CMakeLists.txt file that was intentionally removed in PR #611 artifact cleanup.

Current Failure

CMake Error at CMakeLists.txt:17 (add_subdirectory):
  The source directory /home/runner/work/fortplot/fortplot
  does not contain a CMakeLists.txt file.

Root Cause

• PR cleanup: remove 391 scattered repository artifacts #611 removed root CMakeLists.txt as part of artifact cleanup
• CMAKE CI test still tries to build using obsolete CMAKE configuration
• This blocks ALL PRs including PR refactor: consolidate 9 redundant pcolormesh tests into 2 comprehensive tests #612 which is unrelated

Impact

• CRITICAL: All PRs blocked by failing CMAKE CI
• PR refactor: consolidate 9 redundant pcolormesh tests into 2 comprehensive tests #612 cannot merge despite being technically valid
• CMAKE test validates obsolete build system

Required Fix

Either:

1. REMOVE CMAKE CI test entirely (recommended - CMAKE support was removed)
2. UPDATE CMAKE test to use proper cmake example directory only
3. DISABLE CMAKE CI test temporarily

Context

• CMAKE example in doc/cmake_example/ still works and is valid
• Main project now uses FPM build system exclusively
• This affects PR refactor: consolidate 9 redundant pcolormesh tests into 2 comprehensive tests #612 pcolormesh consolidation waiting for merge

Priority

CRITICAL - Blocks all development work via CI failure

[krystophny]

RESOLVED: CMAKE CI test has been disabled with proper documentation.

TECHNICAL EVIDENCE:

• CMAKE CI test commented out in .github/workflows/ci.yml
• Added documentation explaining CMAKE build system removal
• All PRs now unblocked from CMAKE CI failure
• PR fix: resolve test_blocking_backends directory creation failure (fixes #637) #639 merged successfully after CMAKE fix

ROOT CAUSE CONFIRMED:
Root CMakeLists.txt was intentionally removed in artifact cleanup PR #611. CMAKE example still referenced root directory causing CI failure.

SOLUTION:
CMAKE CI test disabled until CMAKE example can be reworked to be self-contained. Added clear documentation for future restoration path.

CMAKE CI blocker eliminated - all PRs can now proceed through CI.