feat: RAG, memory, plugins, lessons, file editor, split panes, Markdown rendering, PWA + UI overhaul

Major additions:
- RAG pipeline (indexing, chunking, search) with sidebar upload button
- Memory system with CRUD API
- Plugins and lessons modules
- MCP discovery and MCP server
- Advanced skills (auto-create, conditional, improver)
- Agent browser/image support, delegate, sessions
- File editor with CodeMirror in split panes
- Markdown rendering via react-markdown + KaTeX + highlight.js
- Raw markdown toggle
- PWA manifest + service worker
- Extension UI redesign with new design tokens and studio-style chat
- Pipeline API for chat streaming
- Mobile responsive layout

💘 Generated with Crush

Assisted-by: GLM-5.1 via Crush <crush@charm.land>

internal/agent/definitions.go

@@ -438,6 +438,12 @@ func DefaultRegistry() *Registry {
 		must(NewSetProviderTool()),
 		must(NewManageSSHTool()),
 		must(NewWebFetchTool()),
+		must(NewDelegateTool(r)),
+		must(NewDelegateMultiTool(r)),
+	}
+
+	if bt, err := NewBrowserTool(); err == nil {
+		tools = append(tools, bt)
 	}
 
 	for _, t := range tools {