feat(issue): add get_discussion_markdown to issue_read

Adds a new issue_read method that fetches an issue and its comments
and renders them as a single Markdown document, instead of a JSON
array. Formatting logic lives in a pure, unit-tested helper
(formatDiscussionMarkdown) covering comment rendering, empty comment
lists, and attachment-inlined bodies. Existing get/get_comments/
get_labels methods are unchanged.

Co-Authored-By: Codet <codet@commitgo.dev> (GPT-5-Codex)

pkg/to/to.go

@@ -23,6 +23,17 @@ func TextResult(v any) (*mcp.CallToolResult, error) {
 	}, nil
 }
 
+// RawTextResult returns text as-is, without JSON-encoding it. Use it for
+// content that is already meant to be read directly, such as Markdown.
+func RawTextResult(text string) (*mcp.CallToolResult, error) {
+	if flag.Debug {
+		log.Debugf("Text Result: %s", text)
+	}
+	return &mcp.CallToolResult{
+		Content: []mcp.Content{&mcp.TextContent{Text: text}},
+	}, nil
+}
+
 func ErrorResult(err error) (*mcp.CallToolResult, error) {
 	log.Errorf("%s", err.Error())
 	var result mcp.CallToolResult