Release 1.2.7

[Manho]

Summary

• bump Panelize from 1.2.6 to 1.2.7
• document removal of the retired Claude model override workaround
• record upgrade cleanup and regression coverage for the native Claude model-selection path

Verification

• Release Prep workflow passed: https://github.com/Manho/Panelize/actions/runs/29566971588
• release metadata is limited to the five required files
• both generated ZIP artifacts contain manifest.json version 1.2.7
• generated packages do not contain the retired Claude request-interceptor files

After this PR is merged, run the Release Publish workflow with version 1.2.7 and this PR number.