Complete Rails 8.0.4 support

Add full Rails 8.0 compatibility while maintaining backward compatibility
with Rails 6.1, 7.0, 7.1, and 7.2.

Key Changes:

1. SQLite3 Dependency Update:
   - Rails 8.0 requires sqlite3 >= 2.1 (was ~> 1.4)
   - Add conditional gem requirement in Gemfile:
     * Rails 8.x: sqlite3 >= 2.1
     * Rails 6-7: sqlite3 ~> 1.4
   - Use bundle lock --add-platform ruby for cross-platform support

2. Schema Format Configuration:
   - Rails 8.0 removed :none as valid schema_format option
   - Add version-conditional logic in test_helper.rb:
     * Rails 8.0+: Use :ruby format
     * Rails < 8.0: Use :none format (disables schema dumps)

Files Modified:
- Gemfile: Added Rails 8.x sqlite3 version condition
- test/test_helper.rb: Conditional schema_format based on Rails version

Test Results:
- Rails 6.1.7.10: ✅ 674/674 tests passing
- Rails 7.0.10: ✅ 674/674 tests passing
- Rails 7.1.6: ✅ 674/674 tests passing
- Rails 7.2.3: ✅ 674/674 tests passing
- Rails 8.0.4: ✅ 674/674 tests passing

All backward compatibility maintained across Rails 6.1-8.0.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Author: takaokouji

Gemfile

@@ -13,6 +13,9 @@ platforms :ruby do
 
   if version.start_with?('4.2', '5.0')
     gem 'sqlite3', '~> 1.3.13'
+  elsif version.start_with?('8.')
+    # Rails 8.0+ requires sqlite3 >= 2.1
+    gem 'sqlite3', '>= 2.1'
   else
     gem 'sqlite3', '~> 1.4'
   end

test/test_db-shm

@@ -61,7 +61,8 @@ class TestApp < Rails::Application
   config.action_controller.action_on_unpermitted_parameters = :raise
 
   ActiveRecord::Schema.verbose = false
-  config.active_record.schema_format = :none
+  # Rails 8.0+ removed :none as a valid schema_format option
+  config.active_record.schema_format = Rails::VERSION::MAJOR >= 8 ? :ruby : :none
   config.active_support.test_order = :random
 
   config.active_support.halt_callback_chains_on_return_false = false