feat: add MethodConf CMS staging DNS

[glitchedmob]

Routes cms-staging.methodconf.com through the existing public cluster edge alongside staging.methodconf.com.

[github-actions]

Terraform plan

Artifacts: https://github.com/sgfdevs/infra-dns/actions/runs/31335977185

Show summary

CHANGE	RESOURCE
add (1)	module.methodconf_com.cloudflare_dns_record.core["cms_staging"]

Decrypt artifacts:
openssl enc -d -aes-256-cbc -pbkdf2 -in tfplan.enc -out tfplan -pass pass:$OUTPUT_ENCRYPTION_KEY
openssl enc -d -aes-256-cbc -pbkdf2 -in tfplan.txt.enc -out tfplan.txt -pass pass:$OUTPUT_ENCRYPTION_KEY