feat(frontend): restyle home page hero to match official Manus layout

[Simpleyyt]

Summary

Restyles the home page to follow the official Manus app's hero layout (centered greeting + large serif heading + task input + suggestion chips), based on a live visual review of manus.im.

• HomePage.vue: hero block is now vertically and horizontally centered; small serif greeting line ("Hello, {name}") above a large serif heading ("What can I do for you?"); content column narrowed to 680px; added a centered row of pill-shaped suggestion chips (Create slides / Build website / Design / Create games) with a "More" chip that reveals four extra chips (Analyze data / Research / Write report / Create spreadsheet). Clicking a chip fills the input with a localized prompt starter and focuses the textarea.
• ChatBox.vue: placeholder changed to "Assign a task or ask anything"; attach button restyled from a bordered paperclip to a borderless "+" icon button; exposes a focus() method for the chip interaction.
• en.ts / zh.ts: new i18n keys for the placeholder, chip labels, and chip prompt starters (both locales).

Demo

manus_style_homepage_demo.mp4

Official reference	Restyled home page
Official Manus reference	Restyled homepage

Testing

• npm run type-check — pass
• npm run lint — pass (0 errors, pre-existing warnings only)
• npm run test — 36/36 pass
• npm run build — pass
• Manual GUI testing via dev stack (./dev.sh up -d): verified hero layout, chip hover states, chip → prompt fill + focus, "More" expansion, send-button activation.

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