feat(agents): add ruby-reviewer

Add a Ruby and Rails code reviewer agent covering Active Record query
safety, strong parameters, unsafe reflection and deserialization, XSS,
safe migrations, and RSpec/Minitest quality. It builds on the existing
rules/ruby/* and rails-patterns skill.

- Register it in .opencode/opencode.json with a matching prompt file
- Map ruby and rails to it in the orch-review workflow
- Bump the documented agent count from 68 to 69 across README, AGENTS.md,
  plugin manifests, and translated docs

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

.opencode/opencode.json

@@ -288,6 +288,17 @@
         "edit": false
       }
     },
+    "ruby-reviewer": {
+      "description": "Expert Ruby and Rails code reviewer specializing in idiomatic Ruby, Active Record query safety, Rails security defaults, and RSpec/Minitest quality.",
+      "mode": "subagent",
+      "prompt": "{file:prompts/agents/ruby-reviewer.txt}",
+      "tools": {
+        "read": true,
+        "bash": true,
+        "write": false,
+        "edit": false
+      }
+    },
     "rust-reviewer": {
       "description": "Expert Rust code reviewer specializing in idiomatic Rust, ownership, lifetimes, concurrency, and performance.",
       "mode": "subagent",