feat(03-03): add typed path params and per-plugin rollback

Compile regex and enum constraints at route registration so malformed and unknown IDs share a 404, and named rollback errors isolate one plugin's history.

Co-authored-by: Cursor <cursoragent@cursor.com>

pact/capabilities.go

@@ -39,6 +39,8 @@ type HasMiddleware interface {
 type Router interface {
 	Group(prefix string, middleware []string, fn func(Router))
 	Get(path string, handler http.HandlerFunc, middleware ...string)
+	Where(param, pattern string)
+	WhereIn(param string, values ...string)
 }
 
 // HasRoutes is implemented by plugins that declare HTTP routes.