Migrate the PHPDoc authoring skill into a portable domain-owned payload #76

Outcome

Extract the PHPDoc authoring procedure from DevTools into a dedicated fast-forward-phpdoc skill shipped by Code Standards. This is a bounded subtask of #4 and the partial procedure handoff from php-fast-forward/dev-tools#195; those broader issues remain open.

Acceptance

• Read and record the real .agents/skills/phpdoc-code-style source and immutable provenance, including the local/remotely published revision distinction.
• Preserve useful semantic guidance while updating short summaries, abstract interface contracts, restrained BCP 14, useful tag descriptions, supported refinements and inheritance preservation to the user's current requirements. No concrete implementer names or implementation accidents in interface promises; no invented positive-float alias.
• Ship a self-contained dedicated payload under resources/skills, with its own MIT license and relative references. Keep formatting/check execution in the existing Code Standards skill; do not claim a formatter can enforce semantic RFC obligations.
• Update skill discovery/catalog links and the repository's sole-skill instruction proportionately. Prove both Git and Composer archives retain every canonical PHPDoc skill reference and exact license bytes.
• No global skill installation/copy, skill-sync, new runtime dependency, DevTools modification or consumer migration. Propose the legacy handoff after a reviewed release; do not remove the DevTools source now.
• Independent exact-tree review and actual relevant checks before publication; main base without an unnecessary stack. No release/tag publication.