fix(frontend): address CodeRabbit follow-ups from #3276 and #3303 (#3311)

Co-authored-by: FandacqkaCorp <275647464+FandacqkaCorp@users.noreply.github.com>
Co-authored-by: Claude Sonnet 5.5 <noreply@anthropic.com>

frontend/biome.json

@@ -47,8 +47,7 @@
         "useGenericFontNames": "off",
         "useKeyWithClickEvents": "off",
         "useMediaCaption": "off",
-        "useSemanticElements": "off",
-        "useValidAnchor": "off"
+        "useSemanticElements": "off"
       },
       "complexity": {
         "noForEach": "on",

frontend/src/components/sidebar/Sidebar.vue

@@ -17,7 +17,7 @@
       >close</i>
     </div>
     <div v-if="showPwaInstall" class="button release-banner">
-      <a type="button" @click="installPwa">{{ $t("pwa.install") }}</a>
+      <button type="button" @click="installPwa">{{ $t("pwa.install") }}</button>
       <i @click="dismissPwaInstall" role="button" tabindex="0" aria-label="close-banner" class="material-symbols">close</i>
     </div>
     <SidebarSettings v-if="isSettings"></SidebarSettings>