feat(VExpansionPanelTitle): add hover prop to disable hover effect

[selfAnnihilator]

Resolves #21615

Adds hover boolean prop to VExpansionPanelTitle (and VExpansionPanel via prop spreading) to disable the hover overlay effect without relying on custom CSS.

Changes:

• VExpansionPanelTitle.tsx — hover prop (default true); toggles v-expansion-panel-title--no-hover class
• VExpansionPanel.sass — .v-expansion-panel-title--no-hover uses tools.layer('trumps') to suppress overlay opacity on hover
• VExpansionPanels.tsx — hover added to pick() and provideDefaults so it cascades to all child panels
• new-in.json — entry added for VExpansionPanels and VExpansionPanelTitle at 4.1.0
• VExpansionPanels.spec.browser.tsx — 3 tests + showcase story

Backwards compatible. Default hover=true preserves existing behaviour.

Markup:

<template>
  <v-app>
    <v-container style="max-width: 600px">
      <p class="mb-2">Default (hover enabled)</p>
      <v-expansion-panels>
        <v-expansion-panel title="With hover" text="Hover to see overlay effect." />
      </v-expansion-panels>

      <p class="mt-6 mb-2">hover=false on panel</p>
      <v-expansion-panels>
        <v-expansion-panel :hover="false" title="Without hover" text="No overlay on hover." />
      </v-expansion-panels>

      <p class="mt-6 mb-2">hover=false on panels (cascades)</p>
      <v-expansion-panels :hover="false">
        <v-expansion-panel title="Panel A" text="Content A" />
        <v-expansion-panel title="Panel B" text="Content B" />
      </v-expansion-panels>
    </v-container>
  </v-app>
</template>

<script>
  export default {
    name: 'Playground',
    setup () {
      return {}
    },
  }
</script>