feat(files): update save_file tool description and enforce size limit for base64 payloads

internal/mcpserver/server.go

@@ -136,7 +136,7 @@ func New(cfg config.MCPConfig, logger *slog.Logger, toolSet ToolSet) http.Handle
 
 	addTool(server, logger, &mcp.Tool{
 		Name:        "save_file",
-		Description: "Store a base64-encoded file such as an image, document, or audio clip, optionally linking it to a thought.",
+		Description: "Store a file and optionally link it to a thought. Supply either content_base64 (≤10 MB) or content_uri (amcs://files/{id} from a prior POST /files upload). For files larger than 10 MB, upload via POST /files first and pass the returned URI as content_uri.",
 	}, toolSet.Files.Save)
 
 	addTool(server, logger, &mcp.Tool{