Add Cloudflare DDNS template

[darshan-Jahagirdar]

Closes #132.

Adds a Portainer template for oznu/cloudflare-ddns with the documented API_KEY, ZONE, SUBDOMAIN, and PROXIED environment options, and updates the README app list.

Validation:

• .\node_modules\.bin\jsonlint Template\template.json --quiet
• Get-ChildItem Template\Stack -File | ForEach-Object { .\node_modules\.bin\yaml-validator $_.FullName }
• git diff --check

[darshan-Jahagirdar]

Validation update for this PR:

npm run pretest
git diff --check

Result: both passed locally. npm run pretest validates Template/template.json with jsonlint.

Note: the repo's npm test YAML step uses Template/Stack/*; on Windows that glob does not expand and the path does not exist, so I used the reliable JSON validation step plus diff whitespace check.