Fix CI comments that name the wrong source of -march=native

[zfergus]

Description

Corrects the CI comments added in #269 and #270 that name MeshFEMCore as a source of -march=native.

• cmake/recipes/meshfem_sparse.cmake downloads MeshFEMCore with DOWNLOAD_ONLY and compiles its own static library, so MeshFEMCore's MESHFEM_NATIVE never runs in our build.
• The comments in cuda.yml, continuous.yml, python.yml, coverage.yml, and docs.yml now name the actual sources: FindSIMD (SIMD_CXX_FLAGS) and Tight-Inclusion's own target.

Impact:

• Comment-only. No behavior change.

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

• The diff changes only # comment lines, and all five workflows parse as YAML.
• Each workflow triggers on its own file, so CI on this PR exercises them unchanged.

Test Configuration:

• OS and Version: macOS 26.6.2
• Compiler and Version: n/a (comment-only change)

Checklist

• I have followed the project style guide
• My code follows the clang-format style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[zfergus]

Superseded by #272, which includes these comment fixes along with the x86-64-v3 CI change.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.93%. Comparing base (101332c) to head (ef490e3).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #271   +/-   ##
=======================================
  Coverage   96.92%   96.93%           
=======================================
  Files         194      194           
  Lines       17348    17350    +2     
  Branches      944      944           
=======================================
+ Hits        16815    16818    +3     
+ Misses        533      532    -1     

Flag	Coverage Δ
unittests	96.93% <ø> (+<0.01%)	⬆️

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