test: complete Phase 3 - remove AI-specific test files and verify unified plugin management

- Delete ai_integration_test.go and ai_http_integration_test.go as AI plugins should follow same testing patterns as other plugins
- Update GetPluginsByCategory to handle missing extension.yaml file gracefully in test environments
- Rewrite TestAIPluginManagement as TestUnifiedPluginManagement using standard ExtManager interface
- All tests now pass with unified plugin management approach
- Remove AI-specific testing code that violated plugin system consistency

Author: KariHall619

.gitignore

@@ -31,3 +31,5 @@ e2e/server.csr
 e2e/server.crt
 
 atest
+
+*.md

cmd/server.go

@@ -438,7 +438,7 @@ func postRequestProxy(proxy string) func(w http.ResponseWriter, r *http.Request,
 	}
 }
 
-func startPlugins(storeExtMgr server.CompositeManager, stores *server.Stores) (err error) {
+func startPlugins(storeExtMgr server.ExtManager, stores *server.Stores) (err error) {
 	for _, store := range stores.Data {
 		if store.Disabled || store.Kind == nil {
 			continue