feat(mcp): add describe_tools and annotate_tool functionality

* Implement DescribeTool for listing available MCP tools with annotations.
* Add UpsertToolAnnotation and GetToolAnnotations methods for managing tool notes.
* Create tool_annotations table for storing tool usage notes.

internal/app/static_assets.go

@@ -12,6 +12,7 @@ var (
 
 	faviconICO = mustReadStaticFile("favicon.ico")
 	homeImage  = mustReadStaticFile("avelonmemorycrystal.jpg")
+	iconImage  = tryReadStaticFile("icon.png")
 )
 
 func mustReadStaticFile(name string) []byte {
@@ -22,3 +23,11 @@ func mustReadStaticFile(name string) []byte {
 
 	return data
 }
+
+func tryReadStaticFile(name string) []byte {
+	data, err := fs.ReadFile(staticFiles, "static/"+name)
+	if err != nil {
+		return nil
+	}
+	return data
+}