refactor: prepare vue components for vapor mode (#38798)

Removes what would block a later switch to Vue's vapor mode:
`vue-chartjs` and the `SvgIcon` render function are virtual DOM
components, and `v-memo` has no vapor equivalent. This does not adopt
vapor mode, which will be stable in upcoming Vue 3.6.

`vue-chartjs` was a thin wrapper over chart.js, so a local
`ChartCanvas.vue` replaces it. Chart data and options move into computed
values to keep their object identity, which is what `v-memo` was
compensating for.

`chartjs-adapter-dayjs-4` is moved first-party, just ~40 lines that are
easy to maintain.

web_src/js/components/DashboardRepoList.vue

@@ -1,6 +1,6 @@
 <script lang="ts" setup>
 import {computed, nextTick, onMounted, shallowRef, useTemplateRef, type ShallowRef} from 'vue';
-import {SvgIcon} from '../svg.ts';
+import SvgIcon from './SvgIcon.vue';
 import {GET} from '../modules/fetch.ts';
 import {urlQueryEscape} from '../utils/url.ts';
 import type {SvgName} from '../svg.ts';