Fix mismatched VS Code debug launch environments

[rupayon123]

Fixes #5526.

When VS Code launch generation uses the default environment, the debugger may select a build_type = debug environment while the executable and toolchain metadata came from default_envs. Generate those two launch paths from the selected debug environment, while preserving the normal environment metadata used by other IDE files. If debug metadata is unavailable, fall back to the environment whose metadata was generated so the launch entry remains internally consistent.

Validation:

• Added regression coverage for the split-environment case and metadata fallback; both focused tests pass on Python 3.14.
• Black, isort, Pylint, codespell, and git diff --check pass for the changed files.
• The existing VS Code CLI initialization test began installing a second platform/toolchain and did not complete; it is not claimed as passing. The full suite and Windows debugger session were not run.

Prepared with AI assistance; the patch and focused test results were reviewed before submission.

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