docs(roles): add argument_specs and README for traefik, authentik, drawio, garage, nextcloud

Each of the five roles touched in this branch now ships:

* meta/argument_specs.yml: typed schema for every variable in
  defaults/main.yml plus the optional inputs surfaced via this
  branch (traefik_extra_hosts, authentik_host_rewrite_domains,
  authentik_proxy_apps.mode / .allowed_groups, drawio_extra_domains,
  drawio_authentik_forward_auth*, garage_webui_authentik_forward_auth*).
  All five specs load cleanly through ansible-core's
  ArgumentSpecValidator.

* README.md: replaces the ansible-galaxy boilerplate (where it was
  still in place) with a focused write-up — service vars, required
  secrets, ForwardAuth/idempotency notes, dependencies, and a working
  example playbook. authentik and garage READMEs are rewritten to cover
  the new knobs while preserving their existing content.

roles/authentik/meta/argument_specs.yml

@@ -0,0 +1,193 @@
+---
+argument_specs:
+  main:
+    short_description: Deploy authentik (server + worker + Postgres) via Docker Compose.
+    description:
+      - Renders a Compose stack for authentik with traefik labels, optional
+        TLS and a configurable split-horizon host-rewrite that keeps the OIDC
+        issuer URL on the canonical public hostname even when traffic enters
+        on an internal FQDN.
+      - Provisions resources through templated blueprints
+        (local users, groups, OIDC/Proxy/LDAP apps, outposts, OAuth sources).
+    options:
+      docker_compose_base_dir:
+        type: path
+        default: /etc/docker/compose
+      docker_volume_base_dir:
+        type: path
+        default: /srv/data
+      authentik_service_name:
+        type: str
+        default: authentik
+      authentik_docker_compose_dir:
+        type: path
+        description: Defaults to C({{ docker_compose_base_dir }}/{{ authentik_service_name }}).
+      authentik_docker_volume_dir:
+        type: path
+        description: Defaults to C({{ docker_volume_base_dir }}/{{ authentik_service_name }}).
+
+      authentik_domains:
+        type: list
+        elements: str
+        required: true
+        description:
+          - FQDNs the authentik router accepts. The first entry is the
+            canonical (public) hostname and is used for the network alias,
+            the X-Forwarded-Host rewrite target, and as the default OIDC
+            issuer. Further entries cover internal C(*.int.*) names used
+            for server-to-server traffic.
+      authentik_host_rewrite_domains:
+        type: list
+        elements: str
+        default: []
+        description:
+          - Hostnames that should reach authentik but make it generate URLs
+            (OIDC issuer, password reset links, etc.) as if the request had
+            arrived on C(authentik_domains[0]).
+          - Each entry gets its own traefik router and a URL-based
+            loadbalancer service that disables passHostHeader and pins
+            X-Forwarded-Host via middleware. Used for split-horizon setups
+            where the LAN keeps server-to-server traffic but the iss claim
+            must match the public hostname browsers see.
+      authentik_image:
+        type: str
+        default: ghcr.io/goauthentik/server:2026.2.2
+      authentik_port:
+        type: int
+        default: 9000
+      authentik_secret_key:
+        type: str
+        required: true
+        description: PG fernet key / signing secret. Generate with C(openssl rand -base64 60).
+
+      authentik_postgres_image:
+        type: str
+        default: postgres:16-alpine
+      authentik_postgres_db:
+        type: str
+        default: authentik
+      authentik_postgres_user:
+        type: str
+        default: authentik
+      authentik_postgres_password:
+        type: str
+        required: true
+
+      authentik_traefik_network:
+        type: str
+        default: proxy
+      authentik_backend_network:
+        type: str
+        default: backend
+      authentik_use_ssl:
+        type: bool
+        default: true
+
+      authentik_log_level:
+        type: str
+        choices: [trace, debug, info, warning, error]
+        default: info
+      authentik_error_reporting_enabled:
+        type: bool
+        default: false
+
+      authentik_proxy_apps:
+        type: list
+        elements: dict
+        default: []
+        description:
+          - Proxy/ForwardAuth applications rendered via the
+            C(blueprint-proxy-app.yaml.j2) template.
+        options:
+          slug:
+            type: str
+            required: true
+          name:
+            type: str
+            required: true
+          internal_host:
+            type: str
+            description: Required when C(mode=proxy).
+          external_host:
+            type: str
+            required: true
+          mode:
+            type: str
+            choices: [proxy, forward_single, forward_domain]
+            default: forward_single
+            description:
+              - "C(proxy): the outpost itself proxies traffic to internal_host."
+              - "C(forward_single): a single app behind an external reverse
+                proxy via ForwardAuth."
+              - "C(forward_domain): wildcard mode — one provider guards every
+                host on a cookie domain."
+          allowed_groups:
+            type: list
+            elements: str
+            description:
+              - If set, PolicyBindings are emitted (one per group, OR-evaluated).
+                Users in none of the listed groups are denied.
+          skip_path_regex:
+            type: str
+          flows:
+            type: dict
+            description: Authentication / authorization / invalidation flow slugs.
+
+      authentik_proxy_outposts:
+        type: list
+        elements: dict
+        default: []
+
+      authentik_ldap_apps:
+        type: list
+        elements: dict
+        default: []
+      authentik_ldap_outpost:
+        type: dict
+        default: {}
+
+      authentik_oidc_apps:
+        type: list
+        elements: dict
+        default: []
+
+      authentik_entra_sources:
+        type: list
+        elements: dict
+        default: []
+      authentik_login_sources:
+        type: list
+        elements: dict
+        default: []
+      authentik_identification_stage_name:
+        type: str
+        default: default-authentication-identification
+      authentik_login_user_fields:
+        type: list
+        elements: str
+        choices: [username, email, upn]
+        default: [username, email]
+        description: Local login fields shown on the login screen. Empty list hides local login.
+
+      authentik_groups:
+        type: list
+        elements: dict
+        default: []
+      authentik_local_users:
+        type: list
+        elements: dict
+        default: []
+
+      authentik_removed_oidc_apps:
+        type: list
+        elements: str
+        default: []
+        description: OIDC application slugs scheduled for deletion.
+      authentik_removed_proxy_apps:
+        type: list
+        elements: str
+        default: []
+      authentik_removed_local_users:
+        type: list
+        elements: str
+        default: []