mastodon: tighten resources, robust exec tasks, and env defaults

- resources: per-service cpus/mem/pids for mastodon/streaming/sidekiq/redis/db
- compose: rename service key to "mastodon" (was: web), set service_name blocks
- tasks(01_setup): run rails db:migrate via docker exec (non-tty, login shell)
- tasks(02_administrator): healthchecks for 'mastodon', sed with absolute path,
  tootctl as user 'mastodon' (non-tty), optional re-health wait
- env.j2: add RAILS_ENV={{ ENVIRONMENT | default('production') }}
- resource.yml.j2: fix get_app_conf path (service_name default spacing)
- docs: remove outdated Installation/Administration files

Context: https://chatgpt.com/share/68d332a0-ae98-800f-b418-c0d0262eaa2e

roles/web-app-mastodon/templates/env.j2

@@ -8,6 +8,8 @@ ALTERNATE_DOMAINS="{{ domains['web-app-mastodon'][1:] | join(',') }}"
 SINGLE_USER_MODE={{ applications | get_app_conf(application_id, 'single_user_mode') }}
 ALLOWED_PRIVATE_ADDRESSES="{{ MASTODON_ALLOWED_PRIVATE_ADDRESSES }}"
 
+RAILS_ENV={{ ENVIRONMENT }}
+
 # Debug
 {% if MODE_DEBUG | bool %}
 RAILS_LOG_LEVEL=debug