chore: ignore Finder metadata and clarify template validation

.changelog/ignore-finder-metadata.md

@@ -0,0 +1,6 @@
+---
+category: fixed
+type: patch
+---
+
+Remove tracked Finder metadata and ignore .DS_Store files throughout the repository.

.gitignore

@@ -1,2 +1,3 @@
 /vendor/
 /.agents/
+.DS_Store

DESIGN.md

@@ -32,7 +32,7 @@ Runtime images live in `data/` so excluding consumer documentation from a Compos
 
 ## Validation
 
-Install the development tool with `composer install --no-scripts`, then run `php tests/generate-fixture.php`. Composer allows only the official `phpdocumentor/shim` plugin, which installs the signed phpDocumentor PHAR; no runtime dependency is added to template consumers. The CI matrix renders the fixture with PHP 8.3, 8.4 and 8.5 from both the checkout and a Git archive, and actionlint validates the workflow. The PHAR's bundled dependencies are outside Composer's dependency-audit coverage; use this build tool only with trusted project sources.
+Install the development tool with `composer install --no-scripts`, then run `php tests/generate-fixture.php` and `php tests/verify-consumer-skill.php`. The specifically approved `phpdocumentor/shim` plugin installs the signed phpDocumentor PHAR; no runtime dependency is added to template consumers. The separately approved `llm/skills` plugin synchronizes the contribution skill according to `skills.json`, including when `--no-scripts` is used. The CI matrix renders both fixtures with PHP 8.3, 8.4 and 8.5 from the checkout and a Git archive, and actionlint validates the workflow. The PHAR's bundled dependencies are outside Composer's dependency-audit coverage; use this build tool only with trusted project sources.
 
 Generate the fixture from `tests/fixture` with phpDocumentor 3: