Keep README installation and usage current #49

Problem

The README installation example pins an old release line and mixes current usage
with extraction history, source trials and future-oriented language. The Composer
runtime paragraph also suggests that a normal development dependency is resolved
independently of the consumer's dependency graph.

This is a focused follow-up to the already merged README work in #30 / #34,
requested by the user on 26 October. It does not reopen that delivered scope.

Acceptance criteria

• Show normal composer require --dev fast-forward/code-standards, without a
  hardcoded package version or a moving GitHub ref used as a Composer constraint.
• Explain supported present behavior and real runtime compatibility without
  extraction history, promises or release snapshots in the usage guide.
• Preserve current capabilities, manually maintained content and valid local links.
• Validate the unversioned installation in a disposable consumer and execute its
  installed binary; record the actual resolved version instead of promising it.
• Preserve Composer constraints and consolidated changelog history.

Independent PR to main; no tag or release publication is part of this issue.