Redact secret assignments in logs and suggestions

[Widthdom]

Summary

• Redact underscore-separated API/access key options in global tool logs, including assignment and split-value forms.
• Bound global log and suggestion redaction work with input caps, timeout-bounded regexes, and truncation markers.
• Extend suggestion redaction to common token/API/access key assignments, sampled MCP metadata, CLI suggestion output, and issue-draft titles.
• Return the stored redacted suggestion hash from suggest_improvement and preserve sampled metadata/evidence safely when redaction clones records.

Changelog

• Added security fragments:
  • changelog.d/unreleased/3005.security.md
  • changelog.d/unreleased/3006.security.md
  • changelog.d/unreleased/3070.security.md
  • changelog.d/unreleased/3071.security.md

Validation

• dotnet build CodeIndex.sln -p:UseSharedCompilation=false
• dotnet ./src/CodeIndex/bin/Debug/net8.0/cdidx.dll status --check --json
• dotnet run --project tools/CodeIndex.Changelog -- check
• dotnet test tests/CodeIndex.Tests/CodeIndex.Tests.csproj --no-build --filter 'FullyQualifiedName~GlobalToolLogTests|FullyQualifiedName~SuggestionStoreTests|FullyQualifiedName~McpServerTests|FullyQualifiedName~ProgramCliTests.Suggestions_ExportIssueDrafts' -p:UseSharedCompilation=false
• Codex adversarial review: No blocking/actionable issues found.

Fixes #3005
Fixes #3006
Fixes #3070
Fixes #3071