Resolve C# references against logical partial families

[Widthdom]

Summary

• Resolve C# references against stable logical partial-type family keys while retaining every physical candidate and the physical candidate count.
• Feed the same logical identity into grouped symbol ranking, default/grouped hotspots, inspect, dependencies, and impact without merging unrelated namespaces, kinds, arities, or languages.
• Advance the persisted reference-identity contract to version 9 and cover full/scoped add, remove, rename, move, and prior-contract refresh lifecycles.

Validation

• dotnet build CodeIndex.sln -c Release -p:UseSharedCompilation=false --no-restore — 0 warnings, 0 errors.
• Full Release net8.0 suite — 11,822 passed, 9 skipped, 0 failed.
• Full Release net9.0 suite — 11,342 passed, 426 skipped, 0 failed.
• After incorporating the latest origin/main, the combined Resolve C# references against logical partial families instead of physical declarations #5158/Do not index plain C# primary-constructor parameters as public properties #5157/Fix C# primary constructor property extraction #5168 focused suites passed 6/6 on both net8.0 and net9.0.
• dotnet format CodeIndex.sln --verify-no-changes --no-restore and changelog-fragment validation passed.
• Repository reproduction now reports ProgramRunner as a 21-candidate resolved_group; grouped/default hotspot and symbol ranking attribute 2,433 references to the 72-site QueryCommandRunner family.
• Codex adversarial review round 1 found the missing default-hotspot path; that P1 was fixed with regression coverage. Round 2 found no patch-specific regression or further actionable issue.

Documentation and changelog

• Updated USER_GUIDE.md, DEVELOPER_GUIDE.md, and TESTING_GUIDE.md in English and Japanese.
• Added changelog.d/unreleased/5158.fixed.md.

Follow-ups

• None.

Fixes #5158