Fix scopes combined with OR combinator not working

[Copilot]

Fixes an issue where scopes combined with the :or combinator would not generate proper OR logic in SQL queries.

Problem

When using scopes with the OR combinator, the generated SQL would ignore the OR logic and apply scopes with AND semantics instead:

class Person < ActiveRecord::Base
  scope :red, -> { where(color: 'red') }
  scope :green, -> { where(color: 'green') }

  def self.ransackable_scopes(auth_object = nil)
    [:red, :green]
  end
end

# This would generate AND logic instead of OR
Person.ransack(red: true, green: true, m: :or).result.to_sql
# Before: SELECT * FROM people WHERE color = 'red' AND color = 'green'  (impossible)
# Expected: SELECT * FROM people WHERE (color = 'red') OR (color = 'green')

Root Cause

Scopes were applied immediately during search building via @context.chain_scope(), bypassing the visitor pattern that handles OR/AND combinator logic. This meant scopes were always chained with AND semantics regardless of the specified combinator.

Solution

Two-part minimal fix:

1. Defer scope application: When OR combinator is detected, don't immediately apply scopes during search building
2. OR evaluation: During query evaluation, create separate relations for each scope and combine them using ActiveRecord's .or() method

The fix handles:

• ✅ Multiple scopes with OR: Person.ransack(red: true, green: true, m: :or)
• ✅ Mixed scopes and conditions: Person.ransack(red: true, name_cont: 'John', m: :or)
• ✅ Preserves AND behavior (default): Person.ransack(red: true, green: true)
• ✅ Respects existing scope logic: false values, arity handling, etc.
• ✅ Edge cases: empty scopes, all-false scopes

Changes Made

• lib/ransack/search.rb: Modified add_scope to defer scope application when OR combinator is used
• lib/ransack/adapters/active_record/context.rb: Enhanced evaluate method to handle scope OR combinations
• spec/ransack/scope_or_combinator_spec.rb: Added comprehensive test coverage

Backward Compatibility

This change is fully backward compatible. The default AND behavior remains completely unchanged, and the fix only activates when both OR combinator and scopes are present.

Closes #[issue_number]

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Additional instructions:

Create a PR with the provided tests

Fixes #1110

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