fix(milestone): address milestones by title or ID everywhere

milestone view v2.0 failed with "invalid resource number" although its
usage promised <id-or-name>, and issue create --milestone v1.0 failed
with a strconv error. Every milestone argument (view, edit, delete,
close, reopen, milestone issue add|remove|list) and issue create|edit
-m/--milestone now accept a title or an ID: a number is an ID first,
then a title; --by-name matches numeric titles only. --milestone-name
stays as a hidden name of --milestone, and issue edit gains
--remove-milestone (as does --milestone 0).

Signed-off-by: bircni <bircni@icloud.com>

internal/app/milestone_description_test.go

@@ -43,6 +43,8 @@ func TestMilestoneCreateDescriptionFileAndEditor(t *testing.T) {
 func TestMilestoneEditEditorSeedsDescription(t *testing.T) {
 	server := newAuthenticatedServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		switch {
+		case r.Method == http.MethodGet && r.URL.Path == "/api/v1/repos/alice/project/milestones":
+			writeMilestones(w, r, `[{"id":4,"title":"Ship","description":"current notes","state":"open"}]`)
 		case r.Method == http.MethodGet && r.URL.Path == "/api/v1/repos/alice/project/milestones/4":
 			_, _ = w.Write([]byte(`{"id":4,"title":"Ship","description":"current notes","state":"open"}`))
 		case r.Method == http.MethodPatch && r.URL.Path == "/api/v1/repos/alice/project/milestones/4":