Fix ABBREVIATE strategy to return initials

[iamvalenciia]

Summary

• implement the ABBREVIATE runtime strategy by returning the uppercase initial of each whitespace-separated word
• expose the runtime strategy constant and document the supported behavior
• add coverage for SURNAME, FIRST_NAME, and the PhEye/NER person path, including multi-token and single-token values

Root cause

ABBREVIATE was present in the policy model, but StandardFilterStrategy.GetStandardReplacement(...) had no matching switch arm. Policies could therefore request the strategy, but runtime filters silently fell through to the default redaction behavior.

Impact

Values such as John Smith now produce JS instead of a full redaction token. Because the fix is in the shared standard strategy, dictionary name filters and PhEye use the same behavior.

Validation

• dotnet test tests/Phileas.Tests/Phileas.Tests.csproj --no-restore --verbosity minimal
• .NET 8: 1,094 passed, 0 failed, 5 skipped
• .NET 10: 1,094 passed, 0 failed, 5 skipped

Closes #58

[jzonthemtn]

Thanks @iamvalenciia!