Add canonical member-read references

[Widthdom]

Summary

• Add canonical member_read edges for non-invoking C# enum constants, constants, static readonly fields, static properties, and constant-pattern reads.
• Keep true invocations as call, suppress callable-name collision duplicates, and resolve same-file and cross-file member-read targets.
• Exclude modern member reads from callers, callees, and impact by default while preserving explicit CLI --include-member-reads and MCP includeMemberReads compatibility controls.
• Preserve legacy indexes and their historical call rows without requiring migration.
• Keep full, scoped --files, commit-based, watch-style, and MCP indexing correct when consumers or member-read targets are added, changed, removed, or reused.

Root cause

Qualified C# value/member access was historically classified through the callable-name path, so enum constants and other static value reads could be persisted as call. The initial fix also needed workspace-wide target knowledge during incremental indexing: consumer-only scoped updates could omit cross-file member_read edges, while target-set changes could leave reusable consumers stale.

Validation

• dotnet build CodeIndex.sln -c Release --no-restore -p:UseSharedCompilation=false
• dotnet test tests/CodeIndex.Tests/CodeIndex.Tests.csproj -c Release --no-build --framework net8.0 — 10,971 passed, 0 failed, 7 skipped
• dotnet test tests/CodeIndex.Tests/CodeIndex.Tests.csproj -c Release --no-build --framework net9.0 — 10,497 passed, 0 failed, 420 skipped
• After merging the latest origin/main, repeated the Release build and focused Issue Add a member-read reference kind without breaking legacy call graphs #4894 / MCP contract / language-pagination tests: net8 25 passed; net9 24 passed, 1 expected skip
• dotnet format CodeIndex.sln --no-restore --verify-no-changes --verbosity minimal
• dotnet run --project tools/CodeIndex.Changelog -- check
• git diff --check
• Refreshed the repository index and verified index_matches_workspace: true, graph complete/current, and zero cap hits
• Completed both workflow-permitted Codex adversarial-review rounds and fixed all reported actionable findings, including cross-file collisions, writes, and scoped/watch incremental refresh behavior

Documentation and changelog

• Updated USER_GUIDE.md, DEVELOPER_GUIDE.md, and TESTING_GUIDE.md in their English and Japanese sections.
• Added bilingual fragment changelog.d/unreleased/4894.added.md.

Follow-ups

None.

Fixes #4894