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/controllers.md

@@ -0,0 +1,164 @@
+# Controllers - DHH Rails Style
+
+<rest_mapping>
+## Everything Maps to CRUD
+
+Custom actions become new resources. Instead of verbs on existing resources, create noun resources:
+
+```ruby
+# Instead of this:
+POST /cards/:id/close
+DELETE /cards/:id/close
+POST /cards/:id/archive
+
+# Do this:
+POST /cards/:id/closure      # create closure
+DELETE /cards/:id/closure    # destroy closure
+POST /cards/:id/archival     # create archival
+```
+
+**Real examples from 37signals:**
+```ruby
+resources :cards do
+  resource :closure       # closing/reopening
+  resource :goldness      # marking important
+  resource :not_now       # postponing
+  resources :assignments  # managing assignees
+end
+```
+
+Each resource gets its own controller with standard CRUD actions.
+</rest_mapping>
+
+<controller_concerns>
+## Concerns for Shared Behavior
+
+Controllers use concerns extensively. Common patterns:
+
+**CardScoped** - loads @card, @board, provides render_card_replacement
+```ruby
+module CardScoped
+  extend ActiveSupport::Concern
+
+  included do
+    before_action :set_card
+  end
+
+  private
+    def set_card
+      @card = Card.find(params[:card_id])
+      @board = @card.board
+    end
+
+    def render_card_replacement
+      render turbo_stream: turbo_stream.replace(@card)
+    end
+end
+```
+
+**BoardScoped** - loads @board
+**CurrentRequest** - populates Current with request data
+**CurrentTimezone** - wraps requests in user's timezone
+**FilterScoped** - handles complex filtering
+**TurboFlash** - flash messages via Turbo Stream
+**ViewTransitions** - disables on page refresh
+</controller_concerns>
+
+<turbo_responses>
+## Turbo Stream Responses
+
+Use Turbo Streams for partial updates:
+
+```ruby
+class Cards::ClosuresController < ApplicationController
+  include CardScoped
+
+  def create
+    @card.close
+    render_card_replacement
+  end
+
+  def destroy
+    @card.reopen
+    render_card_replacement
+  end
+end
+```
+
+For complex updates, use morphing:
+```ruby
+render turbo_stream: turbo_stream.morph(@card)
+```
+</turbo_responses>
+
+<api_patterns>
+## API Design
+
+Same controllers, different format. Convention for responses:
+
+```ruby
+def create
+  @card = Card.create!(card_params)
+
+  respond_to do |format|
+    format.html { redirect_to @card }
+    format.json { head :created, location: @card }
+  end
+end
+
+def update
+  @card.update!(card_params)
+
+  respond_to do |format|
+    format.html { redirect_to @card }
+    format.json { head :no_content }
+  end
+end
+
+def destroy
+  @card.destroy
+
+  respond_to do |format|
+    format.html { redirect_to cards_path }
+    format.json { head :no_content }
+  end
+end
+```
+
+**Status codes:**
+- Create: 201 Created + Location header
+- Update: 204 No Content
+- Delete: 204 No Content
+- Bearer token authentication
+</api_patterns>
+
+<http_caching>
+## HTTP Caching
+
+Extensive use of ETags and conditional GETs:
+
+```ruby
+class CardsController < ApplicationController
+  def show
+    @card = Card.find(params[:id])
+    fresh_when etag: [@card, Current.user.timezone]
+  end
+
+  def index
+    @cards = @board.cards.preloaded
+    fresh_when etag: [@cards, @board.updated_at]
+  end
+end
+```
+
+Key insight: Times render server-side in user's timezone, so timezone must affect the ETag to prevent serving wrong times to other timezones.
+
+**ApplicationController global etag:**
+```ruby
+class ApplicationController < ActionController::Base
+  etag { "v1" }  # Bump to invalidate all caches
+end
+```
+
+Use `touch: true` on associations for cache invalidation.
+</http_caching>