Resolve graph edges by symbol identity instead of folded name

[Widthdom]

Summary

Persist and query resolved target symbol identity so common names do not merge unrelated methods, languages, classes, and test/source files.

Current v1.38.0 evidence / reproduction

• impact Run --exact-name --max-hops 2 --with-paths --limit 3 --json mixes C# methods with a Python run and misattributes path roots.
• callers Run --exact-name --json reports false self/mutual recursion and false cycles between unrelated Run methods.
• deps --path src/CodeIndex/BoundedFile.cs --limit 10 --json creates unrelated source/test dependencies through common names such as Dispose, Seek, and ReadWrite.

Impact

Impact analysis, dependency boundaries, cycle detection, and refactoring decisions can be fundamentally incorrect.

Suggested direction / acceptance criteria

• Persist a resolved target symbol ID/key on reference edges where resolution is unambiguous.
• Include container, qualified name, signature, language, project, and file scope in resolution.
• Preserve ambiguous edges as explicitly unresolved candidates instead of silently merging them.
• Add cross-language and same-name regression fixtures for dependencies, impact, callers, and recursion.

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Dogfooding candidate IDs: Q016, Q017, R002. Verified against cdidx v1.38.0 at commit 2919bfc9b1b83cfa7ae1d964845d0f9ffca002d1.

[Widthdom]

Work started on branch fix-issue4569-4570.