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

internal/gitea/issues_test.go

@@ -101,3 +101,51 @@ func TestCreateIssueComment(t *testing.T) {
 	assert.Equal(t, "hello", comment.Body)
 	assert.Equal(t, "http://example.com/issues/42#comment-7", comment.HTMLURL)
 }
+
+func TestListIssueComments(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		assert.Equal(t, http.MethodGet, r.Method)
+		assert.Equal(t, "/api/v1/repos/o/r/issues/42/comments", r.URL.Path)
+		w.Header().Set("Content-Type", "application/json")
+		_, _ = w.Write([]byte(`[
+			{"id":1,"body":"first","html_url":"http://example.com/issues/42#comment-1","user":{"login":"alice"},"created_at":"2026-05-01T00:00:00Z","updated_at":"2026-05-01T00:00:00Z"},
+			{"id":2,"body":"second","html_url":"http://example.com/issues/42#comment-2","user":{"login":"bob"},"created_at":"2026-05-02T00:00:00Z","updated_at":"2026-05-02T00:00:00Z"}
+		]`))
+	}))
+	defer srv.Close()
+
+	c := gitea.NewClient(srv.URL, "tok")
+	comments, err := c.ListIssueComments(context.Background(), "o", "r", 42)
+	require.NoError(t, err)
+	require.Len(t, comments, 2)
+	assert.Equal(t, int64(1), comments[0].ID)
+	assert.Equal(t, "first", comments[0].Body)
+	assert.Equal(t, "alice", comments[0].User.Login)
+	assert.Equal(t, "bob", comments[1].User.Login)
+}
+
+func TestListIssueComments_Empty(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		_, _ = w.Write([]byte(`[]`))
+	}))
+	defer srv.Close()
+
+	c := gitea.NewClient(srv.URL, "tok")
+	comments, err := c.ListIssueComments(context.Background(), "o", "r", 42)
+	require.NoError(t, err)
+	assert.Empty(t, comments)
+}
+
+func TestListIssueComments_NotFound(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusNotFound)
+		_, _ = w.Write([]byte(`{"message":"issue not found"}`))
+	}))
+	defer srv.Close()
+
+	c := gitea.NewClient(srv.URL, "tok")
+	_, err := c.ListIssueComments(context.Background(), "o", "r", 999)
+	require.Error(t, err)
+	assert.ErrorIs(t, err, gitea.ErrNotFound)
+}