One gitlink without a .gitmodules entry makes Submodules() report every submodule as Unknown with no checked-out SHA #191

What's wrong

GitSubmoduleListBuilder.ApplyStatusAsync (GitIntegration/Builders/GitSubmoduleListBuilder.cs ~L115-130) runs a single git submodule status for the whole repository and, if it fails, returns the gitlinks unannotated.

Failure scenario (reproduced on git 2.43)

Someone commits a nested repository directly (git's "embedded repository" warning), creating a gitlink with no .gitmodules mapping:

• ls-files --stage -z lists 160000 … inner
• git submodule status dies: fatal: no submodule mapping found in .gitmodules for path 'inner', exit 128
• every submodule, including correctly configured ones, comes back with State = Unknown and CheckedOutSha = null.

Why it matters

One stray gitlink wipes the state of every healthy submodule, with nothing telling the caller why. Tools that decide whether to run UpdateSubmodules based on state then act on no information.

Suggested fix

Run git submodule status -- <path> for the mapped gitlinks only (skipping paths absent from .gitmodules), or on failure retry per path, so only the unmapped entry stays Unknown.

Acceptance criteria

• Integration test: a repo with one configured submodule and one unmapped gitlink reports the configured one's real state and SHA, and the unmapped one as Unknown.