Add Rails backend: accounts via magic link, server documents, sharing

The app becomes a Rails 8 application; the Vue frontend moves to
app/frontend and is served through vite_rails.

- Without an account documents stay in the browser (IndexedDB). Sign-in
  is by magic link or the 6-digit code from the same mail; afterwards
  local documents can be uploaded into the account.
- Server documents (/d/<id>) with versioned saves and a single-editor
  lock per browser tab; others see them read-only and follow by polling.
- Sharing via link (works without an account) and via e-mail invitation,
  roles viewer/editor; the owner manages links and people.
- Store gains a read-only mode that blocks all content changes.
- Solid Queue, Cache and Cable share the one PostgreSQL database.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

config/environments/development.rb

@@ -0,0 +1,72 @@
+require "active_support/core_ext/integer/time"
+
+Rails.application.configure do
+  # Settings specified here will take precedence over those in config/application.rb.
+
+  # Make code changes take effect immediately without server restart.
+  config.enable_reloading = true
+
+  # Do not eager load code on boot.
+  config.eager_load = false
+
+  # Show full error reports.
+  config.consider_all_requests_local = true
+
+  # Enable server timing.
+  config.server_timing = true
+
+  # Enable/disable Action Controller caching. By default Action Controller caching is disabled.
+  # Run rails dev:cache to toggle Action Controller caching.
+  if Rails.root.join("tmp/caching-dev.txt").exist?
+    config.action_controller.perform_caching = true
+    config.action_controller.enable_fragment_cache_logging = true
+    config.public_file_server.headers = { "cache-control" => "public, max-age=#{2.days.to_i}" }
+  else
+    config.action_controller.perform_caching = false
+  end
+
+  # Change to :null_store to avoid any caching.
+  config.cache_store = :memory_store
+
+  # Don't care if the mailer can't send.
+  config.action_mailer.raise_delivery_errors = false
+
+  # Make template changes take effect immediately.
+  config.action_mailer.perform_caching = false
+
+  # Set localhost to be used by links generated in mailer templates.
+  config.action_mailer.default_url_options = { host: "localhost", port: 3000 }
+  # mails open at http://localhost:3000/letter_opener
+  config.action_mailer.delivery_method = :letter_opener_web
+  config.action_mailer.perform_deliveries = true
+
+  # Print deprecation notices to the Rails logger.
+  config.active_support.deprecation = :log
+
+  # Raise an error on page load if there are pending migrations.
+  config.active_record.migration_error = :page_load
+
+  # Highlight code that triggered database queries in logs.
+  config.active_record.verbose_query_logs = true
+
+  # Append comments with runtime information tags to SQL queries in logs.
+  config.active_record.query_log_tags_enabled = true
+
+  # Highlight code that enqueued background job in logs.
+  config.active_job.verbose_enqueue_logs = true
+
+  # Highlight code that triggered redirect in logs.
+  config.action_dispatch.verbose_redirect_logs = true
+
+  # Raises error for missing translations.
+  # config.i18n.raise_on_missing_translations = true
+
+  # Annotate rendered view with file names.
+  config.action_view.annotate_rendered_view_with_filenames = true
+
+  # Uncomment if you wish to allow Action Cable access from any origin.
+  # config.action_cable.disable_request_forgery_protection = true
+
+  # Raise error when a before_action's only/except options reference missing actions.
+  config.action_controller.raise_on_missing_callback_actions = true
+end