docs(skills): add PHP command-dispatch skills (acture-php{,-greenfield,-strangler})

[thorwhalen]

Summary

Adds three agent skills for implementing an acture-style command-dispatch layer in PHP systems — the PHP counterpart to the .NET track in #28. Source: docs/research/acture_research_7 -- PHP Tooling for a Command-Dispatch Architecture.

• acture-php (foundational) — maps acture's three primitives to the modern PHP stack (cuyz/valinor + symfony/messenger + a project-owned #[Command] attribute + spiral/json-schema-generator + opis/json-schema), surfaces the framework variants (vanilla / Symfony / Laravel), and routes to the greenfield or strangler-fig path.
• acture-php-greenfield — file-by-file walk-through for a new project: state model → #[Command] attribute → ~120-line attribute-scanning registry → Messenger dispatcher → first command → CLI surface (Symfony Console 7.3 invokable commands) → Pest architecture tests.
• acture-php-strangler — strangler-fig adoption in an existing codebase: Wrap / Enrich / Extract phases, additive #[Command] + #[AsMessageHandler] overlay that never touches legacy call sites, feature-flagged surface activation order, and PHP-specific special cases (Artisan/Console, controllers, Doctrine entities).

Notes

• Follows the established skill conventions: dev-tool-first positioning (hand-write vs package-reuse surfaced per consumer), #[Command] is project-owned, no reflexive composer require mcp/sdk, metadata-is-data-not-code guardrail.
• All three cross-reference each other and the existing acture-* skills (acture-architecture-primer, acture-hard-donts, acture-mcp, acture-ai, the migration-* track), and link to the source research note.
• Steers away from dormant/deprecated tooling (Tactician, Prooph, spatie/data-transfer-object) per the research note's ecosystem-health findings.

Test plan

• Skills appear in the available-skills list with correct trigger descriptions.
• Cross-references resolve to existing skill names and the committed research doc.