chore: document similar-project scan in AGENTS.md; ignore .serena/ (#8)

* chore: document similar-project scan in AGENTS.md; ignore .serena/ and .DS_Store

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* chore: add .shipguard.yml — exclude node_modules, acknowledge upstream JS debt

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* fix: actually ignore .serena/ (prior commit added negation only)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: newblacc <refactor code>
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

.gitignore

@@ -33,4 +33,6 @@ playwright-report/
 coverage/
 
 docs/*
-!docs/screenshots/
+!docs/screenshots/.serena/
+.DS_Store
+.serena/