feat: add Ruby and Rails rules

rules/ruby/patterns.md

@@ -0,0 +1,44 @@
+---
+paths:
+  - "**/*.rb"
+  - "**/*.rake"
+  - "**/Gemfile"
+  - "**/app/**/*.erb"
+  - "**/config/routes.rb"
+---
+# Ruby Patterns
+
+> This file extends [common/patterns.md](../common/patterns.md) with Ruby and Rails specific content.
+
+## Rails Way First
+
+- Start with plain Rails MVC and Active Record conventions for small and medium features.
+- Introduce service objects, query objects, form objects, decorators, or presenters when the model/controller boundary is carrying multiple responsibilities.
+- Name extracted objects after the business operation they perform, not after generic layers like `Manager` or `Processor`.
+
+## Persistence
+
+- Prefer PostgreSQL for multi-host production Rails apps unless the existing platform has a clear reason for MySQL or SQLite.
+- Treat Rails 8 SQLite-backed defaults as viable for single-host or modest deployments, not as an automatic fit for shared multi-service systems.
+- Keep raw SQL behind query objects or model scopes and parameterize every dynamic value.
+
+## Background Jobs And Runtime Services
+
+- Use **Solid Queue** for greenfield Rails 8 apps with modest throughput and simple deployment needs.
+- Use **Sidekiq** when the app needs mature observability, high throughput, existing Redis infrastructure, or Pro/Enterprise features.
+- Use **Solid Cache** and **Solid Cable** when their deployment model matches the app; use Redis when shared cross-service behavior, high fanout, or advanced data structures matter.
+
+## Frontend
+
+- Prefer **Hotwire** with Turbo, Stimulus, Importmap, and Propshaft for server-rendered Rails apps.
+- Use React, Vue, Inertia.js, or a separate SPA when interaction complexity, existing product architecture, or team ownership justifies the extra client surface.
+- Keep view components, partials, and presenters focused on rendering decisions; keep persistence and authorization out of templates.
+
+## Authentication
+
+- Use the Rails 8 authentication generator for straightforward session auth and password reset needs.
+- Use Devise or another established auth system when requirements include OAuth, MFA, confirmable/lockable flows, multi-model auth, or a large existing Devise footprint.
+
+## Reference
+
+See skill: `backend-patterns` for service boundaries and adapter patterns.