[Improvement] Docs: abort symlink sync on duplicate controller basenames

Address cubic review on #493:

- `ruby_ui:sync_controller_symlinks` now detects two gem controllers sharing a
  basename before creating any link and aborts listing the offenders. The docs
  controllers directory is flat, so the second symlink would silently clobber
  the first and one component would ship the wrong JS.
- Fix the missing `rake` prefix on `stimulus:manifest:update` in the
  ruby-ui-stimulus skill.

Author: djalmaaraujo

.claude/skills/ruby-ui-stimulus/SKILL.md

@@ -44,7 +44,7 @@ Building or changing a Stimulus-backed component:
    - `docs/app/javascript/controllers/ruby_ui/<component>_controller.js` is a
      symlink to the gem file above, not a copy. For a brand-new controller, run
      `bin/rails ruby_ui:sync_controller_symlinks` in `docs/` first to create the
-     symlink, then `stimulus:manifest:update` to register it.
+     symlink, then `rake stimulus:manifest:update` to register it.
    - New JS packages go in `gem/package.json` **and** per-component in
      `gem/lib/generators/ruby_ui/dependencies.yml`.
 5. **Update docs & tests** in the same PR: `<component>_docs.rb` and

docs/lib/tasks/ruby_ui.rake

@@ -15,6 +15,15 @@ namespace :ruby_ui do
       abort "No *_controller.js files found under #{gem_root} - is the gem/ checkout present?"
     end
 
+    # The docs controllers directory is flat, so two gem controllers sharing a
+    # basename cannot both be represented - the second symlink would silently
+    # clobber the first and one component would ship the wrong JS.
+    collisions = controller_files.group_by { |p| File.basename(p) }.select { |_, paths| paths.size > 1 }
+    unless collisions.empty?
+      details = collisions.map { |basename, paths| "  #{basename}: #{paths.join(", ")}" }.join("\n")
+      abort "Duplicate controller basenames found under #{gem_root} - rename one of them:\n#{details}"
+    end
+
     controller_files.each do |gem_path|
       gem_path = Pathname.new(gem_path)
       link_path = controllers_dir.join(gem_path.basename)