Add Calibre template

[darshan-Jahagirdar]

Closes #158.

Adds a standalone Calibre Portainer template using the current LinuxServer image, documented GUI/webserver ports, /config volume, and PUID/PGID/TZ/PASSWORD/CLI_ARGS environment settings. The README app list is updated as well.

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.