Let the C++ build fire again (#775)

[Rafael-SOWNet]

.github/workflows/CPPBuild.yml has not run since 2026-01-02. Its path filters are:

paths:
  - "./Sources/Wrappers/AngouriMath.CPP.*/**"

A GitHub path filter is a glob matched against paths relative to the repository root, so a leading ./ matches nothing. This is the identical defect that silenced Benchmark.yml for ninety-eight merged PRs — same commit (f51c7e03), same date, and the story is written up at the top of that file and in #775. Only one of the two was fixed.

Measured, not reasoned

$ gh run list --workflow=CPPBuild.yml --limit 3
2026-01-02T14:24  pull_request  success
2026-01-02T14:13  pull_request  success
2026-01-02T14:07  pull_request  success

Zero runs since. Meanwhile three commits touching exactly the directories it names have merged (4eb94458, dc349c3f, f4807c46), none of them building the C++ wrapper.

The fix, and two additions to the list

The ./ is removed. Two paths are added, each for a reason:

• Sources/AngouriMath/** — the exported native library is compiled from the kernel, so a kernel change is precisely what can break this build. Filtering it out meant the workflow could only ever fire for changes that were already about C++.
• .github/workflows/CPPBuild.yml — so that a change to these filters demonstrates itself rather than being argued about. That is the trick Benchmark.yml used to prove its own fix, and it is why this PR will make the workflow run.

What this PR does not claim

The breakage is measured; the fix is not yet. It will be the moment this is pushed, and the run appearing on this PR is the evidence — which is the whole reason the workflow file is in its own filter list.

Split out of the trimming/NativeAOT work, where it was found, because it has nothing to do with AOT and should not wait on that review.

[Rafael-SOWNet]

Proved, by the thing itself. The description said the breakage was measured and the fix was not, and that the run appearing on this PR would be the evidence. It has:

$ gh run list --workflow=CPPBuild.yml --limit 3
2026-08-23T03:49  fix/cpp-build-path-filter  completed/success     <- this PR
2026-01-02T14:24  issue-620                  completed/success
2026-01-02T14:13  issue-620                  completed/success

Seven months and three weeks between the second row and the first. The workflow fired because .github/workflows/CPPBuild.yml is now in its own filter list, which is the reason it was put there.