refactor: replace vue-bar-graph dependency with inlined SVG chart (#38292)

Inlines the small SVG bar graph into `RepoActivityTopAuthors.vue` (its
only consumer) and drops the `vue-bar-graph` npm dependency.

- Bars render at static height (dropped the grow animation).
- Theme-aware axis color instead of a hardcoded `#555555`.
- Removed the dangling `role="img"`/`aria-labelledby` on the `<svg>`.
- Reserve the chart height so the page does not shift when the component
mounts.

<img width="416" height="110" alt="Screenshot 2026-07-01 at 11 15 25"
src="https://github.com/user-attachments/assets/b2db4d0c-20f1-4345-9951-32a908abfaba"
/>
<img width="419" height="110" alt="Screenshot 2026-07-01 at 11 15 35"
src="https://github.com/user-attachments/assets/853305a5-575f-4a26-ba3b-12fc51081324"
/>

fyi @lafriks

---------

Signed-off-by: silverwind <me@silverwind.io>

package.json

@@ -70,7 +70,6 @@
     "vite": "8.1.0",
     "vite-string-plugin": "2.0.4",
     "vue": "3.5.38",
-    "vue-bar-graph": "2.2.0",
     "vue-chartjs": "5.3.3"
   },
   "devDependencies": {