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/components/RepoCodeFrequency.vue

@@ -21,6 +21,7 @@ import {
   type DayDataObject,
 } from '../utils/time.ts';
 import {chartJsColors} from '../utils/color.ts';
+import {errorMessage} from '../modules/errors.ts';
 import {sleep} from '../utils.ts';
 import 'chartjs-adapter-dayjs-4/dist/chartjs-adapter-dayjs-4.esm';
 import {onMounted, shallowRef} from 'vue';
@@ -78,7 +79,7 @@ async function fetchGraphData() {
       errorText.value = response.statusText;
     }
   } catch (err) {
-    errorText.value = err.message;
+    errorText.value = errorMessage(err);
   } finally {
     isLoading.value = false;
   }