feat(cli): add migrate command to import from other release tools

[BryanFRD]

Description

Add a ferrflow migrate command that generates a FerrFlow config from an existing release tool configuration.

Supported sources

• semantic-release (.releaserc, release.config.js)
• changesets (.changeset/config.json)
• release-please (release-please-config.json)
• standard-version (.versionrc)

Usage

ferrflow migrate              # auto-detect tool
ferrflow migrate --from semantic-release

Output

• Generates a .ferrflow config file with equivalent settings
• Prints a summary of what was migrated and any manual steps needed
• Warns about features that don't have a FerrFlow equivalent

Notes

Lowers the barrier to adoption. Users can switch to FerrFlow without manually rewriting their config.