Fix resolution-aware C# common-call filtering

[Widthdom]

Summary

• Preserve qualified C# common-member calls during extraction instead of discarding them before resolution.
• Suppress only unresolved qualified common-call noise in bare-name references, callers, callees, and hotspot defaults, while retaining resolved edges and allowing explicit completeness opt-ins through CLI and MCP.
• Keep complex and null-conditional receivers out of global fallback resolution, refresh unchanged version-7 C# indexes under extractor contract version 8, and refresh hotspot aggregates when incremental graph resolution changes.
• Preserve compatibility for legacy read-only indexes that do not have the new resolution-evidence columns.

Validation

• dotnet build CodeIndex.sln -c Release --no-restore -p:UseSharedCompilation=false — succeeded with 0 warnings and 0 errors.
• Issue Make qualified C# calls receiver-aware instead of suppressing them by common name #4867 focused tests — 3/3 passed on both net8.0 and net9.0.
• Reference-graph and deferred-hotspot regression tests — 16/16 passed on net8.0.
• Prepared-command cache tests — 37/37 passed on net8.0.
• dotnet run --project tools/CodeIndex.Changelog -- check — validated all 41 current fragments after merging the latest origin/main.
• Local repository index refresh and status --check --json after the final upstream merge — workspace matched, graph/index complete, and reference cap hits were 0.

Documentation and changelog

• Updated USER_GUIDE.md, DEVELOPER_GUIDE.md, and TESTING_GUIDE.md in English and Japanese sections as applicable.
• Added changelog.d/unreleased/4867.fixed.md.

Adversarial review

• Completed the workflow maximum of two Codex adversarial-review rounds.
• Addressed all actionable findings: extractor contract upgrade, legacy read-only compatibility, case-insensitive filtering, complex receiver qualification, partial-query filtering, and incremental hotspot refresh.

Follow-up candidates

• None.

Fixes #4867