feat(skills): Add dhh-rails-style skill for 37signals Rails conventions

Router-pattern skill with sectioned references:
- controllers.md: REST mapping, concerns, Turbo, API patterns
- models.md: Concerns, state records, callbacks, scopes
- frontend.md: Turbo, Stimulus, CSS architecture
- architecture.md: Routing, auth, jobs, caching, config
- gems.md: What they use vs avoid, decision framework

Based on analysis of Fizzy (Campfire) codebase.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

plugins/compound-engineering/skills/dhh-rails-style/references/models.md

@@ -0,0 +1,214 @@
+# Models - DHH Rails Style
+
+<model_concerns>
+## Concerns for Horizontal Behavior
+
+Models heavily use concerns. A typical Card model includes 14+ concerns:
+
+```ruby
+class Card < ApplicationRecord
+  include Assignable
+  include Attachments
+  include Broadcastable
+  include Closeable
+  include Colored
+  include Eventable
+  include Golden
+  include Mentions
+  include Multistep
+  include Pinnable
+  include Postponable
+  include Readable
+  include Searchable
+  include Taggable
+  include Watchable
+end
+```
+
+Each concern is self-contained with associations, scopes, and methods.
+
+**Naming:** Adjectives describing capability (`Closeable`, `Publishable`, `Watchable`)
+</model_concerns>
+
+<state_records>
+## State as Records, Not Booleans
+
+Instead of boolean columns, create separate records:
+
+```ruby
+# Instead of:
+closed: boolean
+is_golden: boolean
+postponed: boolean
+
+# Create records:
+class Card::Closure < ApplicationRecord
+  belongs_to :card
+  belongs_to :creator, class_name: "User"
+end
+
+class Card::Goldness < ApplicationRecord
+  belongs_to :card
+  belongs_to :creator, class_name: "User"
+end
+
+class Card::NotNow < ApplicationRecord
+  belongs_to :card
+  belongs_to :creator, class_name: "User"
+end
+```
+
+**Benefits:**
+- Automatic timestamps (when it happened)
+- Track who made changes
+- Easy filtering via joins and `where.missing`
+- Enables rich UI showing when/who
+
+**In the model:**
+```ruby
+module Closeable
+  extend ActiveSupport::Concern
+
+  included do
+    has_one :closure, dependent: :destroy
+  end
+
+  def closed?
+    closure.present?
+  end
+
+  def close(creator: Current.user)
+    create_closure!(creator: creator)
+  end
+
+  def reopen
+    closure&.destroy
+  end
+end
+```
+
+**Querying:**
+```ruby
+Card.joins(:closure)         # closed cards
+Card.where.missing(:closure) # open cards
+```
+</state_records>
+
+<callbacks>
+## Callbacks - Used Sparingly
+
+Only 38 callback occurrences across 30 files in Fizzy. Guidelines:
+
+**Use for:**
+- `after_commit` for async work
+- `before_save` for derived data
+- `after_create_commit` for side effects
+
+**Avoid:**
+- Complex callback chains
+- Business logic in callbacks
+- Synchronous external calls
+
+```ruby
+class Card < ApplicationRecord
+  after_create_commit :notify_watchers_later
+  before_save :update_search_index, if: :title_changed?
+
+  private
+    def notify_watchers_later
+      NotifyWatchersJob.perform_later(self)
+    end
+end
+```
+</callbacks>
+
+<scopes>
+## Scope Naming
+
+Standard scope names:
+
+```ruby
+class Card < ApplicationRecord
+  scope :chronologically, -> { order(created_at: :asc) }
+  scope :reverse_chronologically, -> { order(created_at: :desc) }
+  scope :alphabetically, -> { order(title: :asc) }
+  scope :latest, -> { reverse_chronologically.limit(10) }
+
+  # Standard eager loading
+  scope :preloaded, -> { includes(:creator, :assignees, :tags) }
+
+  # Parameterized
+  scope :indexed_by, ->(column) { order(column => :asc) }
+  scope :sorted_by, ->(column, direction = :asc) { order(column => direction) }
+end
+```
+</scopes>
+
+<poros>
+## Plain Old Ruby Objects
+
+POROs namespaced under parent models:
+
+```ruby
+# app/models/event/description.rb
+class Event::Description
+  def initialize(event)
+    @event = event
+  end
+
+  def to_s
+    # Presentation logic for event description
+  end
+end
+
+# app/models/card/eventable/system_commenter.rb
+class Card::Eventable::SystemCommenter
+  def initialize(card)
+    @card = card
+  end
+
+  def comment(message)
+    # Business logic
+  end
+end
+
+# app/models/user/filtering.rb
+class User::Filtering
+  # View context bundling
+end
+```
+
+**NOT used for service objects.** Business logic stays in models.
+</poros>
+
+<verbs_predicates>
+## Method Naming
+
+**Verbs** - Actions that change state:
+```ruby
+card.close
+card.reopen
+card.gild      # make golden
+card.ungild
+board.publish
+board.archive
+```
+
+**Predicates** - Queries derived from state:
+```ruby
+card.closed?    # closure.present?
+card.golden?    # goldness.present?
+board.published?
+```
+
+**Avoid** generic setters:
+```ruby
+# Bad
+card.set_closed(true)
+card.update_golden_status(false)
+
+# Good
+card.close
+card.ungild
+```
+</verbs_predicates>