Fix homepage Counter examples for Vue Vapor and Octane

[ywenhao]

Summary

Fixes the homepage code switcher in the "Familiar code, native machinery" section so each framework tab shows its idiomatic authoring model.

Closes #244

Changes

• Vue Vapor: replace TSX Counter.tsx with a Vue SFC example (<script setup> + <template>), matching in-repo apps like apps/hero-vue-sfc/app.vue.
• Octane: replace plain TSX with TSRX @{ ... } syntax (Counter.tsrx), matching Octane TSRX basics.
• Solid: unchanged (Counter.tsx).
• Update the code card filename when switching tabs (Counter.tsx / Counter.vue / Counter.tsrx).

Test plan

• Open the homepage and switch Solid / Vue Vapor / Octane tabs on the Counter code card.
• Confirm Vue tab shows SFC template syntax and filename Counter.vue.
• Confirm Octane tab shows TSRX @{ } syntax and filename Counter.tsrx.
• Confirm Solid tab still shows the original TSX example and filename Counter.tsx.

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