Actionable v1.0.0

First feature-complete release of the clean-slate rebuild.

Added

• Action model — Actionable::Action + Runner; ordered, inherited step DSL.
• Three outcomes — Success, Failure, and Skipped, with success? / failure? / skipped? / ok? predicates.
• Control flow — succeed / fail / skip and the ! (record + halt) forms, plus halt!; exceptions propagate.
• Typed input/output — FieldStruct schemas; strict-success output validation (:invalid_output), :invalid_input short-circuit.
• Composition — nested action steps (:input / :expose), case_step branching, :if / :unless guards.
• Lifecycle hooks — on_success / on_failure / on_skip / always.
• History & measurement — measure :all, cascading, Oj serialization.
• Registry, optional Rails adapter (transactional, ProxyValidator), optional RSpec integration (perform_actionable, stubs).
• Types & docs — Sord/RBS/YARD toolchain, Actionable::RBS.generate, doctested README/USAGE.

See CHANGELOG.md. Not published to a gem host — git release only.