feat(cli): add overlay upgrade command for upgrading to Overlay 1.1.0

[TristanSpeakEasy]

Summary

Adds the openapi overlay upgrade CLI command for upgrading Overlay documents from 1.0.0 to 1.1.0.

Follow-up to #130 which added full Overlay 1.1.0 support to the overlay package.

Changes

New CLI Command: overlay upgrade

# Preview upgrade (output to stdout)
openapi overlay upgrade my-overlay.yaml

# Upgrade and save to new file
openapi overlay upgrade my-overlay.yaml upgraded-overlay.yaml

# Upgrade in-place
openapi overlay upgrade -w my-overlay.yaml

Files Changed

• cmd/openapi/commands/overlay/upgrade.go: New upgrade command implementation
• cmd/openapi/commands/overlay/root.go: Register upgrade command
• cmd/openapi/commands/overlay/README.md: Add upgrade command documentation
• overlay/README.md: Update documentation for 1.1.0 release

Features

• Upgrades overlay version from 1.0.0 to 1.1.0
• Validates overlay before and after upgrade
• Supports stdout, file output, and in-place (-w) modes
• Shows status messages (upgrade performed or already at target version)
• Clears redundant x-speakeasy-jsonpath: rfc9535 (now default in 1.1.0)

Testing

• All CI checks pass
• CLI command tested manually with test fixtures

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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