Enable strict TypeScript, add errorMessage helper (#37292)

Enable full TypeScript `strict` mode and fix issues discovered during
this refactor. Introduced a `errorMessage` helper function to cleanly
extract a error messages from the `unknown` type.

Signed-off-by: silverwind <me@silverwind.io>
Co-authored-by: Claude (claude-opus-4-7) <noreply@anthropic.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

web_src/js/features/repo-issue-list.ts

@@ -2,6 +2,7 @@ import {updateIssuesMeta} from './repo-common.ts';
 import {toggleElem, queryElems, isElemVisible} from '../utils/dom.ts';
 import {html, htmlRaw} from '../utils/html.ts';
 import {confirmModal} from './comp/ConfirmModal.ts';
+import {errorMessage} from '../modules/errors.ts';
 import {showErrorToast} from '../modules/toast.ts';
 import {createSortable} from '../modules/sortable.ts';
 import {DELETE, POST} from '../modules/fetch.ts';
@@ -87,7 +88,9 @@ function initRepoIssueListCheckboxes() {
         await updateIssuesMeta(url, action, issueIDs, elementId);
         window.location.reload();
       } catch (err) {
-        showErrorToast(err.responseJSON?.error ?? err.message);
+        // FIXME: this logic (including updateIssuesMeta) is not right, should refactor to our JSONError framework
+        const e = err as {responseJSON?: {error: string}};
+        showErrorToast(e.responseJSON?.error ?? errorMessage(err));
       }
     },
   ));