fix: use text/plain for default text mime type

Author: DaleSeo

crates/rmcp/src/model/content.rs

@@ -297,7 +297,7 @@ impl ContentBlock {
         ContentBlock::Resource(EmbeddedResource::new(
             ResourceContents::TextResourceContents {
                 uri: uri.into(),
-                mime_type: Some("text".to_string()),
+                mime_type: Some("text/plain".to_string()),
                 text: content.into(),
                 meta: None,
             },

crates/rmcp/src/model/resource.rs

@@ -193,7 +193,7 @@ impl ResourceContents {
     pub fn text(text: impl Into<String>, uri: impl Into<String>) -> Self {
         Self::TextResourceContents {
             uri: uri.into(),
-            mime_type: Some("text".into()),
+            mime_type: Some("text/plain".into()),
             text: text.into(),
             meta: None,
         }