Finalize mail and Nextcloud bootstrap for Traefik/k3s deployment

[Copilot]

This updates the mail and cloud deployment assets so a fresh server can generate working Docker Compose configs and convert them more cleanly toward k3s/Traefik. It also makes the required secrets and environment contract explicit for mail routing, Nextcloud, storage, and database setup.

• Mail routing and compose correctness

  • Corrects Traefik TCP router behavior for mail protocols by distinguishing plain TCP/STARTTLS ports from implicit TLS passthrough ports.
  • Exports the full mail port set needed by compose-to-k8s tooling: SMTP, submission, IMAP, IMAPS, POP3, POP3S, and Sieve.
  • Keeps the mail service aligned with the existing Traefik ingress model instead of relying on Docker-only assumptions.

• Fresh-server bootstrap hardening

  • Makes init-mail.sh and init-cloud.sh fail fast on missing required env values.
  • Uses stable repo-root-relative paths so the scripts can be run from a clean checkout without depending on caller cwd quirks.
  • Creates expected runtime directories up front for mail and Nextcloud volumes.

• Mail storage initialization

  • Makes S3-backed mail storage opt-in and explicit.
  • Verifies s3fs mounts before continuing, and surfaces mount errors instead of silently proceeding.
  • Clarifies the local-storage path when S3 bootstrap is not requested.

• Nextcloud config generation

  • Replaces ad-hoc sed patching of an existing Nextcloud config with generation of a dedicated hermes.config.php from template values.
  • Adds overwrite/trusted proxy settings needed for Traefik path-prefix deployment and fresh installs.
  • Removes deprecated external_links usage from the cloud compose definition.

• Environment and operator docs

  • Adds the missing HERMES_MODEL_CLOUD_MARIA_IP template entry required by the model/cloud topology.
  • Documents MUST-NOT-BE-EMPTY variables across common, mail, cloud, ingress, and model env files.
  • Adds concise startup, k3s generation, and troubleshooting guidance to the README.

Example of the generated Nextcloud bootstrap config shape:

$CONFIG = array (
  'htaccess.RewriteBase' => '/cloud',
  'overwrite.cli.url' => 'https://mail.example.org/cloud',
  'overwritehost' => 'mail.example.org',
  'overwriteprotocol' => 'https',
  'overwritewebroot' => '/cloud',
  'redis' => [
     'host' => 'hermes-model-redis',
     'port' => 6379,
  ],
  'trusted_proxies' => array (
    0 => '10.42.0.0/16',
  ),
);