fix(ruby): fix TargetRubyVersion and add Rails CI note

Fix TargetRubyVersion from 3.4 to 3.1 (matches container). Add note
about Rails rspec needing a dedicated CI job with database services.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: matthew-on-git

content/docs/standards/ruby.md

@@ -37,7 +37,7 @@ require:
   - rubocop-performance
 
 AllCops:
-  TargetRubyVersion: 3.4
+  TargetRubyVersion: 3.1
   NewCops: enable
   Exclude:
     - "db/schema.rb"
@@ -156,3 +156,4 @@ repos:
 - **`reek` runs as part of `make lint`.** It detects code smells (feature envy, too-many-instance-variables, data clump, etc.).
 - **`sorbet` is optional.** Projects can incrementally adopt it by adding `# typed:` sigils to Ruby files. The `sorbet-runtime` gem provides runtime type annotations.
 - **All tools are pre-installed in the dev-toolchain container.** Do not install them on the host.
+- **Rails rspec in CI:** The dev-toolchain container handles static analysis (rubocop, reek, brakeman, bundler-audit) but Rails integration tests typically need a database service (Postgres, MySQL). In CI, run a separate rspec job with the project's own `ruby` image, Bundler, and a database service. The DevRail `make _test` target handles rspec for simple cases; use a dedicated CI job when your tests require external services.