v0.3.0 — a body of its own for every skill

Changed

• Every skill has a body of its own. 43 of the 44 SKILL.md bodies were
  seven shared templates, so ## Use when could not tell an agent which skill
  to load (#17). All 44 are now distinct, each drawn from its own
  reference.md (or, for the onboarding skills, from bin/symfony-context
  and the command map).
• Validation commands per skill. The Skill Operating Checklist appended
  to each reference.md carried the same design checklist and failure modes
  everywhere. Each file now ends with a ## Validation commands section
  specific to its subject, read-only wherever possible.

Fixed

• strategy-pattern: the export example used #[TaggedLocator], removed in
  Symfony 8.0. It now uses #[AutowireLocator].

CI

• bun run lint fails when two skills share the same ## Use when and
  ## Default workflow, so a skill copied from a template cannot ship again.

Thanks to @DorianMarechal for measuring and reporting the shared bodies in #17.