Make caller ranking precedence explicit

[Widthdom]

Summary

• Make --rank-by count use raw reference count as the true primary caller/callee ordering.
• Centralize deterministic ranking precedence and publish the applied recipe in CLI JSON and MCP structured responses.
• Cover large count differences, ties, test filtering, multiple paths, human/JSON output, and pagination stability.

Validation

• dotnet restore CodeIndex.sln --locked-mode
• dotnet build CodeIndex.sln -c Release --no-restore -p:UseSharedCompilation=false
• make lint
• dotnet format --verify-no-changes --no-restore CodeIndex.sln
• dotnet run --project tools/CodeIndex.Changelog --no-restore -- check
• Final focused caller/callee CLI, MCP, and Issue Make caller ranking precedence explicit and reproducible #4881 tests: 73 passed on net8.0 and 73 passed on net9.0
• Full net8.0 CI-equivalent shards were attempted; the index-command shard passed, while the remaining shard exposed only existing timing-sensitive failures. The Avoid overhead that makes parallel batch slower than sequential #4872 case passed alone, and the watcher case is tracked by Stabilize net8 subproject watcher reconciliation for ancestor .gitignore changes #4955.
• The full net9.0 suite was attempted; its only failure was the existing watcher timeout tracked by Investigate net9 ancestor .gitignore watcher reconciliation timeout #4966.
• Mandatory Codex adversarial review completed. The first pass found one recipe/SQL exact-case mismatch; it was fixed with regression coverage, and the final pass found no additional actionable issue.

Documentation and changelog

• Updated the English and Japanese sections of USER_GUIDE.md and TESTING_GUIDE.md.
• Added changelog.d/unreleased/4881.fixed.md.

Follow-up references

• Stabilize net8 subproject watcher reconciliation for ancestor .gitignore changes #4955
• Investigate net9 ancestor .gitignore watcher reconciliation timeout #4966

Fixes #4881