Add repository RLS scopes with context support

[bnlucas]

Motivation

• Introduce repository-level row-level security (RLS) support so repository queries can be constrained by tenant/user context.
• Ensure all delegated ActiveRecord-like methods are routed through a configurable base relation so RLS enforcement is centralized.
• Provide a simple API to pass context into repository queries, enabling with_context usage or per-call context:.
• Document usage and add specs to prevent regressions and clarify the intended behavior.

Description

• Add rls_scope(&block) class method to store a repository-level scope block and base_relation(context:) to return either model or the executed scope using instance_exec.
• Change delegate_common_model_methods to call base_relation(context:) and accept a context: keyword for delegated methods so queries go through the RLS layer.
• Add with_context(context) and a ContextProxy class that forwards common AR methods while injecting the provided context into delegated calls.
• Update README.md with an example using rls_scope and with_context, and add specs in spec/gaskit/repository_spec.rb covering default model behavior, applied RLS scopes, and context passing.

Testing

• Added and updated spec/gaskit/repository_spec.rb with tests for default behavior, applying the RLS scope, and passing context into the scope block.
• Attempted to run bundle exec rspec spec/gaskit/repository_spec.rb but the run failed because the environment lacks the Bundler/rspec executables.
• No automated tests were executed successfully in this environment due to the missing test dependencies.
• Local/CI environments with bundle install should be able to run the updated specs to confirm behavior.

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Codex Task