Add optional grammatical gender

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Summary

• add optional language-independent grammatical gender metadata to LexiconTerm
• limit the initial categories to feminine, masculine, and neuter without storing language-specific articles or provenance
• preserve source and binary call-site compatibility with a defaulted initializer parameter
• document the boundary and Codable compatibility

Validation

• Swift Format format-and-lint and strict lint passed
• swift package dump-package
• swift build
• swift test (9 tests)
• consumer setup validation passed for AgentGuidelines 0.0.33
• DocC generation passed
• generic iOS and tvOS builds passed
• markdown wrapping, AgentGuidelines provenance, .gitignore template parity, symlinks, and git diff --check passed

Compatibility evidence

• legacy entry JSON without grammaticalGender decodes with nil
• all three values round-trip
• existing initializer calls default to nil
• equality and hashing include gender
• a legacy entry representation ignores the new key when decoding newly encoded JSON
• no CloudKit record schema or app-specific article model is changed

The new API is pure value metadata, so the package remains intentionally log-silent.

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Reasoning Relay exact-head review: APPROVED

• Reviewed base: b08c131561355a18026501bf1d952df07f91fd4e
• Reviewed head: 58fddf6fbe7e9c470a11f1d0c2471392b7add3c8
• Blocking findings: None
• Response hash: ad802e60d929030194619882b143f40065825f3b5ca919822d02ec792e725701
• Payload hash: 211cc76567f9c7b32a950cda63299243baae6b71d24bd28932ff98c1aedbf29f