feat: add issue_list_comments tool (closes #32)

Lists all comments on an issue or PR via GET /api/v1/repos/{owner}/{repo}/issues/{index}/comments.
Read-only, allowlist-gated. Extended IssueComment struct with user/timestamps populated by the list endpoint.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/gitea/issues.go

@@ -141,9 +141,30 @@ func (c *Client) SetIssueState(ctx context.Context, owner, repo string, number i
 }
 
 type IssueComment struct {
-	ID      int64  `json:"id"`
-	Body    string `json:"body"`
-	HTMLURL string `json:"html_url"`
+	ID        int64  `json:"id"`
+	Body      string `json:"body"`
+	HTMLURL   string `json:"html_url"`
+	User      User   `json:"user,omitempty"`
+	CreatedAt string `json:"created_at,omitempty"`
+	UpdatedAt string `json:"updated_at,omitempty"`
+}
+
+// ListIssueComments fetches all comments on an issue or pull request.
+// Per Gitea, /issues/{index}/comments serves both since PRs share index space with issues.
+func (c *Client) ListIssueComments(ctx context.Context, owner, repo string, index int) ([]IssueComment, error) {
+	p := fmt.Sprintf("/api/v1/repos/%s/%s/issues/%d/comments", owner, repo, index)
+	body, status, err := c.GetJSON(ctx, p)
+	if err != nil {
+		return nil, err
+	}
+	if err := MapStatus(status, body); err != nil {
+		return nil, err
+	}
+	var comments []IssueComment
+	if err := json.Unmarshal(body, &comments); err != nil {
+		return nil, err
+	}
+	return comments, nil
 }
 
 // CreateIssueComment posts to /issues/{index}/comments. Per Gitea, this same endpoint