Add API, migration, and browser verification skills

README.md

@@ -109,6 +109,12 @@ than assuming the delegate can fetch it itself.
 - `grounded-article-jsonld` -- generate Article structured data only from
   observed page facts, validate it at every boundary, and serialize it safely
   for additive script injection.
+- `api-contract-design` -- design predictable, evolvable API and module
+  contracts before implementation, including errors and compatibility.
+- `safe-deprecation-and-migration` -- replace and retire APIs, services, and
+  database shapes through measured, reversible, expand-contract cutovers.
+- `browser-runtime-verification` -- verify browser-facing changes with real
+  visual, DOM/accessibility, console, network, and performance evidence.
 
 ## Provenance
 
@@ -125,6 +131,7 @@ each skill's frontmatter:
 - [JuliusBrussee/caveman](https://github.com/JuliusBrussee/caveman) (MIT;
   evaluated, no skill retained)
 - [citeworthyio/seo-agent](https://github.com/citeworthyio/seo-agent) (MIT)
+- [addyosmani/agent-skills](https://github.com/addyosmani/agent-skills) (MIT)
 
 ## Vetting external skills