Implement ecdn rate-limit commands (list/create/get/update/delete)

[clavery]

Summary

The eCDN rate-limit commands were documented but never implemented. These commands would manage rate limiting rules on CDN zones.

Commands to Implement

• b2c ecdn rate-limit list — List rate limiting rules
• b2c ecdn rate-limit create — Create a rate limiting rule
• b2c ecdn rate-limit get — Get a rate limiting rule
• b2c ecdn rate-limit update — Update a rate limiting rule
• b2c ecdn rate-limit delete — Delete a rate limiting rule

Context

Discovered during v1.0 GA readiness audit. Documentation and oclif topic entries were removed in the cleanup PR.