Add Claude Opus 4.7 and Claude Mythos Preview models

[kiro-agent]

This pull request was generated by @kiro-agent 👻

Comment with /kiro fix to address specific feedback or /kiro all to address everything.
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Summary

Adds two new Claude model definitions that were recently added to the Anthropic SDK but were missing from mixtape:

• Claude Opus 4.7 (ClaudeOpus4_7) - Next-generation flagship Claude model (added to Anthropic SDK on April 16, 2026)
• Claude Mythos Preview (ClaudeMythosPreview) - Preview model with advanced capabilities (added to Anthropic SDK on April 7, 2026)

Both models use 200K context / 128K output tokens and InferenceProfile::Global.

Changes

• mixtape-core/src/models/claude.rs - Two new define_model! invocations
• mixtape-core/src/models/mod.rs - Added both models to test_model_ids_are_valid and test_global_inference_profile_models test vectors
• mixtape-core/src/lib.rs - Added both models to the public re-export block

What was tested

• cargo build passes
• cargo clippy passes with no warnings
• All model tests pass (cargo test -p mixtape-core)

Note on GLM 5.5

The original request mentioned "GLM 5.5 from Z AI" but research confirmed no such model exists. GLM 4.7 and GLM 4.7 Flash (already in the repo) remain Z.AI's latest models on Bedrock.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.45%. Comparing base (f4c5b99) to head (7adabc6).

Additional details and impacted files

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##             main       #9   +/-   ##
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  Coverage   88.45%   88.45%           
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  Files         111      111           
  Lines       24212    24216    +4     
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+ Hits        21417    21421    +4     
  Misses       2795     2795           

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