fix(sln): skip solution folders, which are not files (one node per .sln)

[mallyskies]

A solution folder exists only inside the .sln — there's no such directory on disk — so it shouldn't become a node. Visual Studio marks one with the project type GUID 2150E333-8FDC-42A3-9474-1A3956D46DE8 and repeats the name in the path position:

Project("{2150E333-...}") = "Solution Items", "Solution Items", "{C40B...}"   <- folder
Project("{8BC9CEB8-...}") = "jpgfltr", "jpgfltr\jpgfltr.vcproj", "{EA73...}"  <- real project

_PROJECT_RE discarded the type GUID, so the folder became a node with a bare source_file, no directory component, and a null source_location — which no ignore rule can suppress, since there's no path to match.

Supersedes the proj_path == proj_name heuristic from #1789 (absolute-path leak). Skipping the entry closes that leak more directly and keys off the field that states the entry's kind, rather than a coincidence between two others — a real project whose path equals its name would trip the old heuristic, and there's a regression test for that. test_sln_solution_folder_ids_are_relative becomes test_sln_solution_folder_is_not_a_node, keeping the #1789 assertion.

Scope is one node and its contains edge per affected .sln. Nothing dangles: folder GUIDs are never edge endpoints. tests/test_dotnet.py 47 passed.

🤖 Generated with Claude Code

[graphify-labs]

Graphify reviewed this change.

Looks safe to merge — no coupling regressions and no blocking issues, checked against the code graph (not a self-assessment).

Formal verification. No changes could be formally verified in this run.

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Graphify review — findings

Skips solution folders in extract_sln by matching Visual Studio's well-known solution-folder type GUID (captured from the Project(...) type field) instead of the old proj_path == proj_name heuristic, so virtual groupings never become nodes and real projects always resolve to their path. This closes the #1789 username leak more directly — no folder node means no absolute scan path to relativize — and no longer misclassifies a real project whose path equals its name. Updates the tests to assert folders are absent while path-equals-name projects remain nodes.

No blocking issues surfaced. 2 lower-confidence candidates did not survive cross-model review.

Analysis details — impact, health, verification

Impact & health

Graphify review

Impact — 69 functions depend on the 65 functions this change touches.

Health — grade A; no new coupling hotspots.

Verification — 69 functions in the blast radius were not formally verified this run (proofs are advisory here).

Gate & verification

graphify gate

PASS — objectively clean (no health regressions, tests not run — proofs not run this pass (advisory)). Grounded, not self-assessed.

Advisory (not blocking):

• verification_scope: 69 function(s) in the blast radius were not formally verified this run

Formal verification

Could not verify: Could not verify extract\_sln.

The verifier did not have enough to check extract\_sln, so it is saying so rather than guessing. No false assurance is the whole point.

Guarantee: No guarantee either way, this is an honest abstention, not a pass.

Note: Reason: parameter `path` is annotated `Path` — outside the synthesizable primitive/collection set