Lazy-load some Vue components, fix heatmap chunk loading on every page (#36719)

Lazy-load 3 Vue components that are safe to defer (no pop-in effects).
This reduces `index-domready` from 515 KiB to 502 KiB (-2.5%).

The old `vue3-calendar-heatmap` vendor chunk (264 KiB) that previously
loaded on every page is eliminated entirely — it was mostly duplicate
`tippy.js` and `vue` copies that webpack had split out. The actual
heatmap library is only ~12 KiB minified, now inlined into the
`ActivityHeatmap` async chunk.

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Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

web_src/js/features/heatmap.ts

@@ -1,5 +1,4 @@
 import {createApp} from 'vue';
-import ActivityHeatmap from '../components/ActivityHeatmap.vue';
 import {translateMonth, translateDay} from '../utils.ts';
 import {GET} from '../modules/fetch.ts';
 
@@ -46,6 +45,7 @@ export async function initHeatmap() {
       noDataText: el.getAttribute('data-locale-no-contributions'),
     };
 
+    const {default: ActivityHeatmap} = await import(/* webpackChunkName: "ActivityHeatmap" */ '../components/ActivityHeatmap.vue');
     const View = createApp(ActivityHeatmap, {values, locale});
     View.mount(el);
     el.classList.remove('is-loading');