docs(collection): document all roles and fix metadata drift

Replace ansible-galaxy init placeholders across the collection and
correct documentation that drifted from the code, after a multi-agent
review of every role README against its defaults, tasks and templates.

Collection level:
- README: role table for all 16 roles, requirements and role-ordering
- galaxy.yml: declare community.docker and community.general deps,
  real description/tags/urls; normalize license to MIT-0
- meta/runtime.yml: requires_ansible '>=2.15.0'
- plugins/README: document the homarr_layout filter and
  garage_credentials lookup instead of scaffold boilerplate

Per-role meta/main.yml and README for the placeholder roles
(389ds, authentik, authentik_outpost_ldap, base, collabora, drawio,
garage, homarr, httpbin, keycloak, nextcloud, opencloud, traefik).

Correctness fixes found during review:
- keycloak: wrong domain default, drop invented keycloak_cert_resolver,
  document the provisioning feature
- garage: root_domain is .s3.<first-entry>, not the bare domain
- opnform: jwt/front_api secrets use `openssl rand -hex 32`; align the
  validation fail_msg in tasks/main.yml accordingly
- send: S3 example references garage_s3_domains[0] (was singular)
- opencloud: document required opencloud_wopi_domain

License normalized to MIT-0 across galaxy.yml, role meta and READMEs to
match the SPDX headers.

roles/send/README.md

@@ -48,13 +48,17 @@ With S3 (Garage) backend:
 
 ```yaml
 send_storage_backend: s3
-send_s3_endpoint: "http://{{ hostvars['backend']['garage_s3_domain'] }}"
+send_s3_endpoint: "http://{{ hostvars['backend']['garage_s3_domains'][0] }}"
 send_s3_bucket: "send"
 send_s3_access_key: "{{ lookup('digitalboard.core.garage_credentials', 'send', host='backend')['key_id'] }}"
 send_s3_secret_key: "{{ lookup('digitalboard.core.garage_credentials', 'send', host='backend')['secret_key'] }}"
 ```
 
+When `send_storage_backend: s3`, the role asserts that `send_s3_endpoint`,
+`send_s3_bucket`, `send_s3_access_key` and `send_s3_secret_key` are all set,
+and fails early otherwise.
+
 License
 -------
 
-MIT
+MIT-0

roles/send/meta/main.yml

@@ -2,7 +2,7 @@
 galaxy_info:
   author: digitalboard
   description: Deploy a self-hosted Send (timvisee fork) instance with Redis via Docker Compose
-  license: MIT
+  license: MIT-0
 
   min_ansible_version: "2.14"