refactor: rename CI_PNPM_FALLBACK_VERSION to CI_PNPM_FALLBACK_MINOR

The constant holds a minor-level floor (e.g. "9.15"), not a precise pin.
pnpm/action-setup@v4 resolves it to the latest matching patch at install
time, so the name and comment now reflect that behavior accurately.

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

Author: justin808

react_on_rails/lib/generators/react_on_rails/install_generator.rb

@@ -253,13 +253,15 @@ def setup_react_dependencies
         setup_js_dependencies
       end
 
-      # Pinned when the scaffolded CI workflow has to supply a pnpm version because
-      # `pnpm/action-setup` requires one unless package.json declares `packageManager`.
-      # Patch-level pin keeps the drift window inside one pnpm minor series; bump when
-      # the repo's own CI upgrades pnpm. Users can override by committing
-      # `packageManager` to their package.json.
-      CI_PNPM_FALLBACK_VERSION = "9.15"
-      private_constant :CI_PNPM_FALLBACK_VERSION
+      # Minor-level floor used when the scaffolded CI workflow has to supply a pnpm
+      # version because `pnpm/action-setup` requires one unless package.json declares
+      # `packageManager`. `pnpm/action-setup@v4` resolves this to the latest matching
+      # patch (e.g. `9.15` → latest `9.15.x`) at install time, so this is a minor
+      # floor — not a reproducible patch pin. Bump when the repo's own CI upgrades
+      # pnpm. Users who need exact reproducibility should commit `packageManager` to
+      # their package.json instead.
+      CI_PNPM_FALLBACK_MINOR = "9.15"
+      private_constant :CI_PNPM_FALLBACK_MINOR
 
       def add_ci_workflow
         return if options[:pretend]
@@ -292,7 +294,7 @@ def add_ci_workflow
         template("templates/base/base/.github/workflows/ci.yml.tt", ci_path,
                  { package_manager: package_manager, has_lockfile: has_lockfile,
                    package_manager_declared: package_manager_declared,
-                   pnpm_fallback_version: CI_PNPM_FALLBACK_VERSION,
+                   pnpm_fallback_version: CI_PNPM_FALLBACK_MINOR,
                    has_active_record: has_active_record, has_rspec: has_rspec })
         @ci_workflow_generated = true
       end

react_on_rails/spec/react_on_rails/generators/install_generator_spec.rb

@@ -2130,9 +2130,9 @@ class ActiveSupport::TestCase
     # Existing Shakapacker apps skip the seeding path, so the CI scaffold has to pin the
     # version itself or the workflow fails before dependency install.
     it "pins a pnpm version in the setup step" do
-      # Anchor to the constant so silent drift between `CI_PNPM_FALLBACK_VERSION`
+      # Anchor to the constant so silent drift between `CI_PNPM_FALLBACK_MINOR`
       # and the rendered template would fail this test.
-      fallback_version = described_class.send(:const_get, :CI_PNPM_FALLBACK_VERSION)
+      fallback_version = described_class.send(:const_get, :CI_PNPM_FALLBACK_MINOR)
       assert_file ".github/workflows/ci.yml" do |content|
         expect(content).to include("uses: pnpm/action-setup@v4")
         expect(content).to match(