Match the build workflow's Ruby setup in release.yml

The previous attempt kept bundler-cache: true in release.yml and
relied on Bundler.with_unbundled_env to unbundle the child rake. That
also reverted GEM_PATH to its pre-Bundler value, so freetype (only
installed in vendor/bundle) disappeared from the PicoRuby sub-build's
load path and ttf2c.rb failed with "cannot load such file -- freetype".

Follow the working build.yml pattern instead: drop bundler-cache and
install rake / freetype into the system gem path with `gem install`.
The child rake then finds both via the default Gem.path with no
bundler env to inherit in the first place.

Make `require "bundler/setup"` optional in the Rakefile and guard
sh_unbundled with `defined?(Bundler)` so the same Rakefile works for
local `bundle exec rake` and for CI's gem-install setup.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: harukasan

.github/workflows/release.yml

@@ -30,7 +30,9 @@ jobs:
         uses: ruby/setup-ruby@v1
         with:
           ruby-version: '4.0.1'
-          bundler-cache: true
+
+      - name: Install Ruby gems
+        run: gem install rake freetype
 
       - name: Build combined UF2 (firmware + dictionary)
         run: rake

Rakefile

@@ -1,4 +1,11 @@
-require "bundler/setup"
+# Bundler is convenient for local development (ensures the Gemfile gems
+# are on the load path) but not required — CI may install gems globally
+# via `gem install`. Treat its absence as a no-op so the Rakefile works
+# either way.
+begin
+  require "bundler/setup"
+rescue LoadError
+end
 
 PROJECT_DIR = __dir__
 BUILD_DIR   = File.join(PROJECT_DIR, "build")
@@ -18,7 +25,11 @@ end
 # setup and must not inherit BUNDLE_GEMFILE / RUBYOPT from this rake,
 # or they try to load this project's Gemfile and fail.
 def sh_unbundled(*cmd, **opts)
-  Bundler.with_unbundled_env { sh(*cmd, **opts) }
+  if defined?(Bundler)
+    Bundler.with_unbundled_env { sh(*cmd, **opts) }
+  else
+    sh(*cmd, **opts)
+  end
 end
 
 desc "Configure, build and produce combined UF2 (default)"